Soliciting opinions on the necessity of credit card info when only selling

Never an issue selling with a CC on file. Getting paid is a different thing. Agon wants a payment option for fees, either upfront or post sale, but either way there is a listing fee when listing that has to be paid upfront. Having said that, I’m pretty sure you can use PayPal for fees as well, but don’t quote me. 

Thats I think where I was confused about my fees selling on Audiogon.

Audiogon charges fees either upfront or post sale yet you have to pay a fee upfront for the listing.  
I guess your real choice is pay up front then pay up front again or pay up front and then pay again post sale.

Surprised there isn’t a charge somewhere in the middle

Ha, that's funny.
You have to decide which is the best deal. When selling a high priced item, it's probably better to pay a $50 or $100 flat fee rather than be billed hundreds based on percentage after the sale.

It’s not that confusing. Pay in full, flat listing fee AND posted value fee. Or, pay listing fee up front and pay the selling fee after... both are listed clearly to choose. The down side of the former is you only get the listing for 30 days. So, if you exceed that, you have to relist at the same fee. If you choose the latter route, your listing stays up, but your fees can be significantly higher. It pays IMO, to price right upfront for the quick sale.