There can't be a ''what vouch reviews should look like'' because it's not the same if they are reviewing a netflix account, config making, a guide or a refund service. What is appropriate or not is defined by the amount of interest the reviewer put into reviewing the product received. If he got a netflix account I don't think there´s much to it more than saying it´s legitimate. But if you provide them with a guide and they say ´´the guide works, vouch´´ that's just not enough and the person will be warned and forced to change it into a proper review.
Agreed, but a vouch format would be pretty neat to implement tbh.
Speed / Stability / Feature rich / UI friendliness / Support / How long you've tested it for.
I'm just throwing stuff out here, but a rating out of 10 could be used for every category and a comment of why you rated is as you did.
IMO it'd certainly help both buyers and sellers but not sure if anyone else would be a fan of it.