Like SS Steve said, the asking price on line is no way to price. Actual sale price is what to go by, using several sales , averaged. Guys that talk about jumping on gun like a duck on a June bug are crazy. Before anything else condition has to be considered. I use to sell guns to PDs. Took their trade ins on the deals. There can be a wide variation in condition of police trade ins. There will be a few that are mint, a lot bigger percentage that have cosmetic issues. Always a few that are beat. Very few have been worn out from shooting.
While PD trade ins can be excellent deals, buying them on line is iffy. I would say for most guys when you factor in shipping, transfer fees, ect you are better off buying at a LGS.
The $500 isn’t killer it’s average price. I don’t collect service or stainless S&Ws. I do get them on trades and right now in my opinion any S&W service type revolver in Good condition is $500. I also think used S&Ws have topped out. Guys that paid 90% prices for 80% guns are stuck.