Well you have two things really: vouches and vouch copies.
Vouches are usually given after a trade has been (succesfully) completed, to indicate someone has some experience as a trader and can be trusted a bit more (personally I don't value vouches at all: past performance is no guarantee for future results)
Vouch copies are usually being given with eBooks etc.
One person gets the eBook for free and will then (usually) confirm the eBook is as described.