Why don't you contact any or all of those used FB dealers here at this forum itself, to straighten out your problem. All these FB machines are broadly alike, though diff. brands and no brand. Find a mechanic/ Service engineer, who can help you, on payment. Better
begging with a local Sevice Engr.than going after the elusive seller. Probably the machine is ok, but with no Instruction manuals, well an Engineer can decide it.
AND, please do not meddle with it without knowing the assembling and commission, based on 'some' website instruction, you may endup damaging it !
Be patient and get help an expert help from local people, who can crack the nut in the way it should.
LAST: An American USED piece will be still better than an alien brand new, and if you still want to buy a cheap Chinese machine, GO to China, at any of Sign Show, meet them. There are so many good people and good machines at very cheaper price. Select the HONEST Manufacturer, not an agent.
Wish you will come out of it soon.