Thats the reason I made the website in the first place, No KYC, small fee, no funny business. A place for skin buyers and investors alike to make skin transactions.
Right, so don't reinvent the wheel with some sort of escrow system between the buyer and seller.
Just do what bitskins and csdeals does: let them deposit funds to the website and then if they buy a skin they pay with the funds they have on your website.
No need for some sort of escrow transaction between the buyer and seller.
You can do this pretty easily I think. Create a database object for each individual user with a couple objects.
so when they log in to your site with their steamid they have a certain session key or something (not sure how that works with OpenID) that identifies them as steam user X.
now from the site you (the steam user) makes api requests to your server when they visit **steamskins**.com/account/mybalance with a request that includes their session key / openID auth.
that's just a DB query to get their latest balance.
Now if they want to deposit and they don't already have a deposit address and they visit something like steamskins.com/account/deposit, they send an api req with their session key to you requesting an address.
Just use bitcoin core's getnewaddress, link the address with their session ID / steam object, and if they deposit successfully update their balance.
