You need to prove to giffgaff first that you are a good recruiter.
Do you have a good plan on how to get the recruits?
(eg You or a family member may have a shop or You have some kind of arrangement with a Local University or other place where you are likely to get New Members onto the giffgaff Network. )
zgbsgshk How can I get 500 cards at a time? I've seen others get thousands of sheets at a time.
Are you on friendly terms with these other people? Are you able to speak to them for advice?
500 at a time? I'v never heard of anyone being able to order 500 SIMS from their own account in one go.