I don't like the "seller guarantee" like that. It leaves an alterior motive for a seller to undergrade. Lets say I have an ASM 94 and I say its a NM+ 9.6 or better and guarantee if it's lower...I'll give you your money back...ok..so someone buys it for whatever prices, sends it in and it comes back a 9.2. The buyer says, I want my money back..seller refunds..now seller is working with a CGC graded book and can probably get more money for it then non-graded. It's pretty cut and dry, either you take returns regardless..or you don't..don't do some inbetween and say "yeh, if this ONE independant party says it's different then I'll refund"
Brian