I would never take paypal as a payment. They ultimately control the deal after the deal is done. If the buyer says "I bought a widget, but received a wadget, the seller has to prove (to an entity that knows nothing about pinball) that they did not cheat the buyer.
Cash, in hand, in person, or no deal unless the buyer wants to wire the money before picking up the machine. Pinball tends to be a very emotional hobby for many people with many people thinking a used machine should be treated just like a new blender purchase from Walmart.