TripleClick gift cards (http://www.tripleclicks.com/detail.php?item=173941) are perfect to combat this fear. There is ZERO RISK of overselling, because there is no selling... just hand them a card and tell them to check it out!
SFI e-cards are another passive approach which has no cost for those on a tight budget. X-Cards are another affordable option.
All three of these options are relatively passive and shouldn't give the impression of overselling.
