Max,
Good start. RIA has a pretty solid reputation. One question that's easy to answer for yourself, is whether or not the Reserve Price less fees will leave you with a fair return on the sale. Since you've noted this is a "high end" gun, I assume it will be in premium (nationally advertised) auction. Regional auctions feature guns of a lower value offered to more local and limited market size.

"I hate rude behavior in a man. I won't tolerate it" - Capt. Woodrow Call