[JollyElm]

Past sales are definitely a really good starting point if there's enough consistency there.

It's always very helpful to eliminate one or more of the most expensive and least expensive recent sales when determining the average price of similar cards. This will nullify some of the BS high prices coming out of the ridiculous card doctor/shilling d-bags on eBay, as well as the low price aberrations that can occur for a variety of reasons (seller not truly understanding the 'value' of his card when he listed the BIN price, etc.).

The worst part of the past sales conundrum is never being sure what's going to happen tomorrow. Before the COVID explosion of the card market, we all can see now that we would've done extremely well to ignore past sales data and waaay overpay for the big name (for me, post-war) cards - Mantle, Clemente, Mays, Aaron, Ryan, Koufax, etc. - before their prices went crazy. But now that the same market has softened a little/lot, past sales from a couple of months ago are way out of whack with the reality of where prices are probably going today.