Others have mentioned shipping costs as part of the problem so do you
use calculated shipping? It appears that the $9.99 is a flat fee rather
than calculated/variable. USPS Ground Advantage should not be that high
for a single comic book sale.
Keep all transaction information in ebay. Do not take checks or give out
personal information. Probably a scam since you are a new seller selling
an expensive item. Also-since you are doing local pickup, have you tried
FBM or CL to avoid scammers?