It may not be a matter of trusting each other is may be a matter of not wanting to deal with Paypal. Paypal has many rules and some sellers just don't want to deal with those headaches. If you have a Personal account, after a certain number of payments for goods and services you will need to upgrade to a Premier account per the Paypal site. Also as of 2011:
PayPal is required by the IRS to report the sales of goods and services for customers who, in a single year receive:
• More than $20,000, AND
• 200 or more payments.
The new IRS 6050W changes apply to all payment providers, including PayPal. This includes payments received after January 1, 2011, with the first reports sent to the IRS in early 2012. So do you really want Paypal tracking your transactions? Whose to say the rules won't change or one or two large transactions like selling a pinball might trigger the seller to hit one of the thresholds? Some sellers may not want to tie their paypal to a savings/checking account. There are a multitude of reasons.
If you want to buy a machine and use paypal then find a seller who will accept it or move on. Think of it this way if you were selling a machine and had multiple folks interested and one wanted to pay cash and the other paypal which person would you sell to?