This type of thing happens. Alot with Tesoro. I blame the buyers lack of research.
I've seen many sold with description "selling to buy machine with VDI or TID" or "tried in test bed, same tone for dime and iron"
Tesoro are, for now besides the golden and Cortes in sum mode, a one tone machine. There's alot of information in that one tone, but it takes time to learn.
Many new to the hobby want a detectors that practically digs the hole for them. Little do they k ow, in my experience, those bells and whistles can cause you to miss targets if you aren't familiar with the readouts, averaging, differences of soil conditions, etc.
So I see the total of 13 that I've seen sold on the bay as a very small number compared to the fact that they have probably sold tens of thousands of units.
Again I think it's the people that never used a Tesoro and/or don't understand them or are used to the multimeters screen detectors that have resold them quickly.
The gent I bought my 2nd unit from at a steal said he bought it only to run it through the test bed for data reasons in something he's putting together Co.paring cost/depth/separation/disc abilities for every unit he can use. The Mojave being so new, he just bought it, tested it, then sold to me for $30 less than he paid. Full warranty.