If he doesn't have good long Rep, at least 3 to 6 month but 1 year is better, than don't do it. Check the account, when was it made on Sourceop, when was it made for steam, does it look like an active main account or a alt account? Heavy traders with lots of Rep normally can be trusted. Rep on the steam account means nothing, the Rep we are referring to is from sites like sourceop.com. If the account looks like it is new or an alt don't do it.
If you do it and he sends you the money you will get an email from paypal, normally within 3 to 5 minutes of him sending the payment. If he does a charge back your screwed more or less. Its not easy for him to do but it happens. Gift is no longer an option, replaced with sending to a family or friend option.