By just looking at a vouch, you can determine the value of it. Being so, I don't think a free vouch nor a 1-10 dollar vouch, is going to make anyone trust this fellow anytime soon. We all have the ability to read, and the ability to tell the difference between a penny from a one hundred dollar bill. So I think the rule should be vouch templates, for an example;
VOUCH FOR : user name
Value = xx.xx $$$$
What the trade was for? :
Customer's comments. :
This way, we can see things more clearer and skip through the garbage a lot faster. If you just trust the person over how many vouches he/she has, rather than what the vouches are for then this might not matter to you as much.