Used equipment sales are rough right now. The machines aren't valuable enough for it make sense to spend a lot of time in labor to ensure they work and offer a warranty. The cost of shipping and labor makes up about half the value of the equipment.
Miners selling the equipment don't want to sell it for what it's worth, and buyers of the equipment don't want to pay prices of what makes it profitable for people like me to sell.
There is significant demand for used equipment, but people don't want broken machines.
Offering a warranty on a $250-$500 machine is stupid because if and when there are issues with shipping, which there inevitably will be to varying degrees, shipping them back will completely offset any profitability in the transaction.
As a buyer, it is difficult to place an accurate value on used equipment that could potentially have a failure rate of 10%-75% without a warranty. The warranty suggests that the seller has done some testing or due diligence of the equipment
One thing that makes used Whatsminers valuable is that parts can be taken off them and put on newer units. Buying used Whatsminers can allow you to acquire replacement power supplies for the same or lower cost as new power supplies. As machine valuation goes up, it makes a lot more sense to test and fix broken machines.
Used S19 J Pros are valuable because of their ability to underclock, giving you around a similar efficiency as new K Pro models, but on a model that is significantly cheaper and more durable. In the bull market, these units can overclock really well.
Trying to save a dollar on the front end in this industry often results in paying way more on the backend. As a buyer, it is important to really evaluate your partners and the economics of what they are doing. You do not want to place equipment with a host that goes bankrupt.
Many sellers of miners enter into risky transactions, and cannot absorb any transactions that go sideways. A lot of buyers are not aware of the risks they are assuming. I think it's really important for buyers to understand the market dynamics of why things are priced certain ways. I know everyone is super price sensitive right now and wants the lowest price conceivable, but that usually doesn't yield the best results.
We will have a bull market again, and the economics of used hardware will make a lot more sense.