Any way to pay Traders through Steam Wallet ?

buy something for them/buy something from them through the market (fees though)

Not at the moment. There have been rumors of wallet funds becoming tradable, but that wasn't confirmed and there's no guarantee it will happen at all.
EDIT: also what MarvelousMax said.

You can buy TF2 keys.

If you could then people would go crazy stealing accounts/passwords, to get as much money as possible, I'd suppose it would just be easier to not let you trade money than account for theft and people who fake trades.