I dont feel they are selling used miners though....they are profitable so might as well keep running them.  A lot of people around here are building pretty massive mining farms (all S9's).  I cannot stress how stupid that is.  S9's are at the end of their lifecycle and the next generation will probably see the same increase in efficiency as the S7vsS9 (of course a little less).  Profitability is high now, but in 4 months ?  I feel its a gamble,I rather have GPUS, my 2 cents.

Bitmain not only dominates hardware sales but in my opinion has a 51% attack vector already secured in hash rate they control.

I think the easier way to start is with a normal PC with some VGAs to mine Ethereum, you can get four 1060 or 580 (depending on what you want to mine and the cost of electricity on your house).

Did all the payments go to the same wallet? Trace some of the payments on the blockchain to see how they have been spent.

I only got 3 with the kit I purchased!

Wait, yours is running at 100 what? 100*C? turn it off before you destroy it. You should be concerned and finding a solution at 80*C to reduce it, I would be surprised if it lives much longer if you are really that hot.