Binance is complete crap! I cant even login(I use copy paste for the password). Resetting the password is also not possible, because system is busy.
When I try again to reset the password I cant even press the next button.
Did you type the password manually? Try to type it manually and see if it's going to work.
But how do I assure the money comes from the seller and not from a third party?
It's a P2P so basically, the seller will have the fund transferred to you. As long as the transaction will go through and you receive the fund, it's not a matter of concern whether they use a third party or not.