Find someone reputable to accomplish a pre-buy inspection of the helicopter. It needs to be someone who is knowledgeable about the type of machine (EC120) and the engine. it could be a seperate engine inspection and airframe inspection. A borescope inspection would be very important if you are worried about the condition of the engine. I know an owner who is paying over $300,000 USD to repair an engine that had been damaged previous to his purchase. An engine inspection prior to buying the machine would have been very worthwhile.