I don’t know about comic books, but grading is what killed the baseball card hobby. If your card was graded less than 9.5 no one would buy it, unless an older hall of famer card from the 50’s. The more cards you sent at once, the better the grades. It was a scam that killed collecting. Many companies gave away high grades like water. See home shopping channels. Sounds like comics may be different. Go with the best reputation company and only send in ones that are near mint+. My off topic 2 cents/rant. Apologies.