As GOG for example has already a couple of games which are also on Steam but not every trainer will support both platforms (or the retail version). Or the majority of CH members don't like this (or that) platform.
Also, if gift links are the only thing accepted, do you accept ones from the bundle sites (i.e. Indiegala, Groupees, etc...)?
[Edited by EquinoxUniverse, 3/4/2016 2:54:54 AM]
I would assume CD keys are fine too if it doesn't work it just counts as breaking the deal to gift, likely they'd contact you about it but you are still responsible for the key working.
* Updated game trainers and cheats daily
* Get notified when new cheats are added
* Request which games get new trainers
* Priority support with any problem