How much worth are TF2 crates?

Unless they're a salvaged crate series, they're worth literally no more than a cent or two, and you can't do anything with them besides unboxing them.

You can see the value of any item by attempting to sell it on the market and checking current prices of what other people have them listed at.

That being said, crates are worth 1 penny, and even then you may never sell it as there are thousands of most crate series selling for 1 penny :P

I once got a Strange Hitman's Heatmaker for a few crates. Hehe, that was good.

Is selling them on the market worth it?

Not all crates are wortless, I have seen some go for 50bucks or more

Some people manage to sell crates for 1 tf2 weapon but you'll have to wait for a while