Between sales tax, buyer fees, credit card fees, shipping costs, transfer fee at your FFL and sellers fees, the prices just get too high. I try to sell there and have some success, but it’s better for everyone if you contact the seller directly and ask for a direct sale. Alternatively even a local dealer might be able to beat that.
For the gun your looking for, it should be easy to find a dealer with a low price and then call them directly to make a deal.
If it’s a rare or collectible gun, it may be reasonable to pay the extra costs.