Your outrage is appropriate----it's the principal of the thing.
On the other hand, such a conversion is common enough (right up there with reaming out a tenth of an inch of the 38-44 Outdoorsman or Heavy Duty to accommodate 357 ammo)----common, as in "as common as dirt", that one might allow as how a prospective buyer might very well be expected to ask about it---specifically. Then if the auction house chooses to lie about it, we have a whole different situation------------not that anybody's going to do anything about it except for mumble-grumble.
Speaking of mumble-grumble and auction houses, here's some more for you------old news, but certainly worth repeating. Once upon a time----awhile back, ROCK ISLAND AUCTION COMPANY was about to have a Regional Auction. These Regional Auctions were pretty much akin to a garbage disposal at the time, but they'd sent a catalog to me----and I looked at it. Here's a two gun lot----6" .22 caliber 1st Model Single Shot described as junk; and an 8" .38 caliber 1st Model Single Shot described as really SPIFFY!!! Now S&W is said to have made only 160 .38 caliber Single Shots in 6, 8, or 10" barrel lengths, so this is something SPECIAL-----------nowhere near junk. Oh, and by the way, the serial number of this .38 caliber 1st Model Single Shot is listed in N&J. That means it's time to sit up straight and pay attention!!
So I did. I called and started firing questions at the RIA folks. As an aside, and in the interest of at least some brevity, I know what questions to ask. Then I called twice more, talking to different people each time, asking the same questions each time, and got the same answers each time. This is for real!!! I call again, and make an appointment for a "viewing". And when the time came, I jumped in my little car and drove 725 miles (one way) for my viewing.
I arrived, was greeted and ushered in in a manner befitting visiting royalty, and led to a table with both guns laid out for inspection. I asked if I could remove the grips. "Make yourself to home." was the response. I did just that.
This absolutely superb 8" .38 Caliber 1st Model Single Shot was as bogus as a three dollar bill. Each and every response to my previous questions to three different people were out and out lies. My host asked, "Is that what you're after?", and given a negative reply, said "Oh well, there'll always be another auction."
Forewarned is forearmed.
Ralph Tremaine