I like the idea of building a reference system in. One thing to note is that you actually validate the user owns said account on another site. On B/S/T forums

I like the idea of building a reference system in. One thing to note is that you actually validate the user owns said account on another site. On B/S/T forums back in the day, a semi-common "scam" was an impersonating user saying "here's my 1000+ feedback eBay account", which may have the same username but they did not actually own.