The problem with a money order is the buyer has no real recourse if the seller misrepresented the item, it doesn't get shipped, etc. And it isn't just the nefarious seller. Stuff happens in life (health emergency, family issues, etc.) that may prevent the seller from completing the deal or, in bad cases, refund the funds.
With paypal, there is recourse available through them. If you don't get the item, paypal refunds the money. This is why, when I buy, I much prefer paypal.
As a seller, I also prefer paypal though I hate the relatively heavy fees paid by the seller. With paypal, the seller gets paid--no counterfeit anything; no returned check fees assessed against the seller when the buyer's check bounces, etc.
Each to his own. I've bought and sold a lot of stuff to and from individuals over the years and it's been fine--only once did I have a dispute resolved through paypal when the seller didn't ship the item.
Carl