There are a lot of companies out there that are keeping their end of the bargain, but it is up to you to understand the bargains you enter into. We all get burned from time to time but the essence of education is not to let the same thing happen to you over and over.
Realize that every time you lay out money for a shop, you will be reimbursed ONLY if the shop is accepted. Right now, with this economy, there are many many folks out there willing to try their hand at shopping and the attitude of some companies is to just reject the shop and pay you neither fee nor reimbursement rather than try to find some way to make it work. Mostly they won't have a problem finding another shopper to try the shop and a report that has no exceptions is far safer to give a client than a report with minor exceptions.
I have never bothered getting the Gold Certification because shoppers who I have come to trust over the years report getting the same email offers and seeing the same jobs available that I see without it. My understanding is that in some markets, such as the Los Angeles area, there is enough competition from other shoppers that shoppers do find that the Gold Certification gives them an edge on being given jobs. Pay more? No. If I do X job for the client I would receive the same fee and reimbursement as any other shopper whether they are certified or not. The argument generally is that X job is ONLY OFFERED to Gold Certified shoppers and that does not seem to hold up to reality. You build a reputation with a company and once they know you are thorough, accurate and timely you will be selected to do jobs you request more frequently than someone with a lower rating with them (and yes, your shops get scored by every company whether you get to see your score or not).