From that list, HB, Bundle Stars, IG and GMG are safe as far as I know. G2A is a huge no-no, and I don't know about the others.

The general rule of thumb, is to avoid sites with "key" in their name.
Write the URL here: http://keyradar.com/, and see what response you get.

The most commonly used (and trustworthy) sites (that I know of) are:

• Humble Bundle
• Bundle Stars
• Indie Gala
• Games Planet
• Games Republic
• Game Bundle
• Groupees
• Daily Indie Game

I might have missed some smaller sites from that list.
Green Man Gaming had some issues with revoked keys in the past, but now they seem to have been solved.

I use Bundlestars and IG from that list...I used GMG before but I think the site is a mess and the mystery keys thing is kinda shady
g2a should be avoided and I dont know the rest

Kinguin= not a fan.
GMG depending for what. Don't get mystery bundles.
GameBundle is ok

If you want to play it safe, you could take a look at this subreddit: https://www.reddit.com/r/GameDeals/
The sites whose deals are advertised there, have been approved by Reddit's mods.

G2A and CD Keys.com are unofficial resellers, so use with caution, same as if you were buying from a trader (that is exactly what you are doing). Same with kinguin. You can use them as long as you understandwhat they are and the risks which come with it. Bundlestar, Indie Gala, GamersGate, GreenManGaming, Humble Bundle are regular shops and will almost never have issues. Never heard of Dealzon and CDkeyhouse.

Okay I changed up my list now, and got rid of cdkeys.com and cdkeyhouse, and dealzon, and g2a just because i'm not a huge risk taker.but what about gamersgate? Anyone use that one?

G2A and CDKeys.com is a big no-no as it is a grey market store and you risk your gams being revoked.

As for GMG - avoid buying preorders. They are known to put preorders before they get any keys, details or contract only to then change the description and refuse refunds (there has been a cases where GMG put a preorder page saying they will provide steam key only to send Rockstar/GOG/other keys later and frefuse refund, because "well, we didn't send you Steam key but we already sent you other key and we cannot know you didn't use it:)

I don't know Dealzon nor CDkeyhouse.

HumbleBundle, Bundlestars, Gamersgate are official and trustworthy.

So is IndieGala but keep in mind that on IG you should use your key quickly (within 60 Days) because they support keys only for that long. If you buy for yourself it's not a problem. If you want to trade or to make Ga make sure to do so before 60 Days.

https://www.instant-gaming.com/en/

Use this site since one year and no problem so far

You should also consider Amazon; there are a few nice deals there from time to time.

Like many here, I avoid grey market sites like G2A and Kinguin. Personal choice, though.
I'm surprised nobody here has mentioned Nuveem. Personally, I think it's fine as long as you're Brazilian (ordering from Brazil). Otherwise, if you're trying to circumvent their rules with VPN, etc., it's not okay. :)
YMMV.

*Humble Bundle = great

Bundlestar = great AND trades well. 
Indie Gala = good but doesn't trade well cause people join groups and do group-buys to get crazy discounts on bundles
G2A= annoying people tradng to obtain all the worthwhile keys so they can sell them to other players. keys are usually not guaranteed, and the entire service is a detriment to the trading community. 
GamersGate= ? whazzat?
Dealzon = ?
CD Keys.com = ?
CDkeyhouse= ?
GreenManGaming (I've been reading lots of flak against these guys lately) = not sure how this one works but they seem to be legit.

you are missing:
groupees = great and trades well
dailyindiegame = only bought from once but was not ripped off so i guess good :)
hrkgame = no bundles but usually very competitive prices and all the keys i have gotten from them so far work.

kinguin.net

• Humble Bundle: Probably the best site if you are in the ROW region. They often carry DRM-free builds next to selling Steam keys. Sadly, said builds are portable versions, meaning if there is a patch, it is another complete download. But after GOG, they are probably the best digital game store right now.
• Bundle Stars: They really worked hard to carry a lot of high-grade stuff, but usually their bundles and single game packages (also called "bundles") are noteworthy.
• IndieGala: Their store is mediocre in selection and prices, but they are the most generous bundle site. High-tier bundle site, medium-level store.
• G2A: Second-hand market of keys that should not be used yet. Emphasis on "should not be". It is as safe as buying something without receipt on a flea market. And about as legal from their point of view. (But, if you want to support some tax-evaders and a few Eastern European groups specialising on selling cheap keys with a 50-100% profit, go ahead.)
• GamersGate: They have a huge selection of Steam and non-Steam games, and once in a blue moon they get a sale discount on a few high-quality games nobody else can. They also tend to fuck up store prices and tend to run out of keys, in which case you may need weeks to finally get the product. Recommended site, but always check their Tutor section to see which keys have run out again…
• Dealzone: It1s not a store just a site collecting prices from other stores. For video games, use IsThereAnyDeal instead.
• CD Keys.com: Avoid like the plague, unless you want Xbox cards. For some reason they have a steady supply of almost surely illegal but always working cards on those.
• CDkeyhouse: No redeeming factor, stay the hell away.
• GreenManGaming: They are a legit reseller finally and they often carry sick deals, especially on pre-order prices. Their support is featured in many horror stories though. Advised to buy occasionally and one product at a time.

By the way, there are several more bundle sites and online stores you didn't list, from GamesRepublic to Daily Indie Game, Groupees, One More Bundle, OtakuMaker, WinGameStore, Games Planet, FireFlower, and GameFly, to name only a few.

I only buy regularly from IG, Humble Bundle and Bundle Stars.

Then there's Indie GameStand - they do "pay what you want" deals every few days, Flying Bundle, tried them once and all went smoothly, and of course there's Groupees.

Personally, I would avoid sites like CD Keys, CDkeyhouse and such. It's probably a prejudice, but the names/urls alone seem suspicious enough to me.

In my opinion from the best to the worst - my opinion is more on bundles stand point not really sales game to game.

• Humble Bundle - Best games from all bundle sites, you can get from AA to indie at a pretty nice price, and then you can decide where the money goes: charity/devs/humble - The Best imo

• Bundlestars - Pretty nice bundles overall, good prices, nothing much to say really

• Indie Gala - Is great if you Group Buy them, it cuts the price by half or a third, bundles indie games, some bundles have great gems, at the lowest price of them all (with GroupBuys)

• G2A - I would stay away from key re-sellers, just in case, yes it's cheap, yet you're not sure where the people got them, and there's always a a chance (small or not) of getting revoked and stuff, i just don't trust it, it's too shady when you need to buy insurance to get the keys.

The others I Don't really know, but i can add some good-ish sites

• Groupees - Some good pre-order bundles, some not, if you feel lucky go for it.

• DIG (Daily Indie Game) - Great Prices, BTA (that generally is +3 or 4cents) gives you 2 bundles, it has a good price standing point.

• Otakumaker - Now this one is really hard, in one half i really want to like them on the other they are pretty terrible, so ill resume to positives and negatives. Positives = GREAT Prices like really nice 4€ - 60 keys or 6€ 90 keys, thats few cents each key. Some Games are good or have cards and it's always worth it, you have a 98%-97% off with the highest packs. Negatives = Keys take time up to 24h to be delivered, it comes by e-mail if that's an issue, they can't be stored on their website like the other sites. To many or some Freebies included in the bundled, they almost have 6 or 7 games that are pretty nice, and then they put 1 or 2 freebies that are being given away all the time on gleam.io, that really loses the value of the bundle. Last but not the least, bundles take a month or more to be over, so it's slow as f*ck to get new ones. Overall I Kinda like it because they give you a lot for the price, on the other half all those negatives could be improved.

Hope this helps! Myself wasted more on HB > IG > BundleStars > IG > Groupees > DIG.

I preferred indiegala and HB sometime bundlestar is always works for price is lower than steam directly.

Added GA for all your peoples help!

Avoid G2A (and Kinguin) just plain dodgy. I regret giving kinguin my details.

Bundlestars
Indie Gala
GamersGate

yes to these

Out of the ones listed:

Humble Bundle

This is a good one! Also, it supposedly takes a smaller cut (thus the developer gets more from each purchase). No idea if that information is outdated though.

Bundlestar

Also a good one.

Indie Gala

IG has had a bit of a shakey history. While the keys they offer are legitimately obtained, they've not always been upfront with how they handle things, and sometimes even had deceiving descriptions. (their old "Beat the average" that was not actually an average but something that was changed manually is one such case)

G2A

Avoid. Stolen keys often end up here, and even if you get the games cheaper, know that you can't be sure where the key actually comes from. Sometimes it's just a key from a cheaper region, sometimes it's from credit card fraud. And they've shown to be unwilling to actually do something about it.

GamersGate

Another good one. Nothing special about it.

GreenManGaming (I've been reading lots of flak against these guys lately)

GMG has, on several occasions, sold games that they don't actually have the rights to sell, and it's unclear where they got the keys from. CD Projekt was not happy with them selling The Witcher 3, and they've also ended up selling games from Activision where they got the keys from some other source. The keys they sell from Paradox, Valve, Ubisoft and a bunch of other are legitimately obtained though.

This is also a good Place,where i bought much Keys :

https://www.instant-gaming.com/de/

I have also used WinGameStore.com ; Purchased Bioshock Infinite's DLC from there and something else I think.