I compared the auction winning bids (column B) against
https://truegunvalue.com used prices (Column C is used 3rd party price, D is new price, E is either C or, if it not available, 71% of C plus $25)
Column F is the ratio of B to E, and column G adds 13% buyer premium to that. (See the attached PDF.)
For the most part, the winning bid was roughly equal to the used "true gun value" (and the extra 13% would be over that.)
Many action winners spent significantly more, sometimes 1.5 times as much more, as they could elsewhere.
I probably miscalculated quite a few times, but I think it shows the trend.
A few rifles were sold cheap - two Springfield 2020 in .22LR at 50%-ish and Ruger M77 in Win .270 at 75%.
S&W M&P 2.0 with removed firing pin went for 60%, that was a bargain; PDP sold for 80%, Savage MC9MS at just under 90%.
For all others, the deal was not much better than Gun Broker.
And you would have to go to pick up your purchase during the same not particularly convenient or wide time window as the other 150 winners.