Not siding with either person but dust could easily be from them testing them before shipping. Resealed box could be customs or anyone along the shipping path checking the contents.
You will have to let us know if you actually take them to court, curious to the results. One of those he said, she said type arguments, how do you prove it either way?
Why not RMA it with Halong?
I cant help but agree with Buck here but if the miner was new and unopened as the seller stated and the buyer opened the unit and ran it for 5 minutes then it is the buyers problem and buyer should open a ticket with Halong to have it replaced under warranty.
Both the B52 and B29 have to be calibrated out of the box before autotune can be enabled but there is a firmware bug that the miner never completes autotune and unless you manually change it to "Factory" the miner runs in "Performance Mode" and if you have it in a cooling deficient situation I have no doubt it could burn up but that's not the sellers fault.
The item was indeed used as i found dust inside and the box had been resealed