I didn't know this type offer was still around. I can tell you from personal experience we got hammered by refunds as the policies expired. I'm sure your participation will also be subject to 100% chargebacks as were ours . Once we realized how large our liability was we stopped the program but it continued for several years.
I was never able to find a company that didn't require charge back participation and we never tried it again. Looking back it probably cost us some buisness in fixed as customers looked at the refund possibilities verses repairs .
Lesson learned are never repeated