As a buyer, I have no idea why people wouldn't want to use PayPal. Lots of buyer protection as long as you count it as a retail deal and not "friends and family", super easy to use. If you cover the seller fees then sure it costs a few bucks, but so does driving down to the post office, standing around in line, getting your money order, buying a stamp, and driving home after. Not to mention all the extra waiting. Sure, the waiting doesn't usually cost, but isn't getting the part a week or two earlier worth something? It is to me. Not to mention I can handle the entire payment without ever leaving my house and taking time out of my day.
As a seller, it's a little more tricky. PayPal always sides with the buyer first. ALWAYS. So if your buyer is a bit sketchy, or impatient, or one of those people you just can't ever please, then you run the chance of PayPal siding with the buyer over you and sucking the money right out of your account. But, claims are a two sided process. So, if you can prove your case, you still have a shot. And, even if they side with the buyer, they require the parts be returned. So while it may turn into a PIA and cost you some money, it shouldn't be a complete loss.
So yeah, in over 10 years of doing business with Paypal I've had overwhelmingly great experiences, and a couple of neutral experiences. As a buyer it's amazing. As a seller, a couple of precautions go a long way - taking pictures of the item prior to shipping, in the package and the condition of the package before it was shipped, paying for shipping insurance and making sure you get a tracking number and update Paypal with the tracking number. Do that and there's no questions or claims regarding shipping times or if/when the package arrived, and if something gets damaged you have the evidence to defend yourself. Quite honestly, all of that is really necessary as a seller anyway, because the buyer can come after you even if it's not a Paypal transaction. And with cell phone camera's being what they are it takes a couple minutes to do all that anyway.