Some months ago I bought an item from a CR seller who accepted either check or paypal. I sent a check but when I heard from him nothing had arrived I immediately re-paid through paypal. Of course he wouldn't have cashed the check if/when it arrived so there was no risk I'd pay twice, and my concern was to make sure the seller was treated fairly and got his money quickly.
For any non-international US transaction I have found that USPS mney orders are a more secure substitute for cash that does not incur a charge to the seller.
Mitch Harris
Little Rock Canyon, Utah, USA