I dont think this is a great idea. Ultimately it was you
who invited them. You shouldnt be just looking at their ratio proofs or the fact they are 10%. You should also be looking at every single one of their posts. Or at least I would. When was the last time they were in IRC? Did they partake in any other giveaways in the past? If yes, go ask the person who invited them and see if they are doing ok. What kind of user are they? Being 10% and having 2 good ratio proofs isnt enough to determine what the user and potential invitee is like. Also, everyone has different requrirements and expectations of their invitee's. The best users aren't necessarily the first post to apply in a giveaway.