i would say ask for proof but these days, people can easily photoshop proofs.. what you should do however is BELIEVE! What i mean is with the right traffic, you could make 10k+ per week from coupons.. yes from coupons commissions.. its easy math. some coupon pay $1.00 per submit.. now multiply that by getting 20k clicks per week, and only half of those opt-in (in most cases, more than half opt-in).
however, i don't believe in buying sites.. i make new sites, get traffic and monetize while getting traffic. customers/readers do not know how old your site is..