Power them up and do a test print. If that can't be done you are buying blind and your print heads may all be bad. Figure worst case 6k per printer for a new set of heads
I have a couple Mimaki JV3 160s available in good condition. Would be much better printers to start with . They are easier to find parts and service when needed. Let me know if your interested.
Word of advice, don't waste the money. It sounds like you know nothing about wide format printers and their maintenance. Purchasing them without any knowledge of software, fixing, repairing and cost of parts is the dumbest thing you could do.
Spend the money and buy a new valuejet 1638 and make sure to purchase additional training.
There are so many variables and issues that could plague a printer....and my first question would be why does the seller want to sell?