Not all sellers are out to screw over buyers.
There are some other reasons for sellers not wanting to accept paypal.
Some of that is related to the additional fees ($0.30 plus 2.9% of the total payment including shipping). After all, eBay has already taken roughly 5% of the winning bid price not to mention the fees for listing the auction in the first place. But on the other hand, sometimes it is worth the cost of business to use paypal.
Paypal has sort of a SPP - seller protection policy. The theory is that if a seller conforms to the requirements of the SPP, then the seller is protected against scams by the buyer. This is not always true, but in the majority of cases it is better than nothing. However, most of the SPP requirements do at times seem to be nothing more than jumping through unnecessary hoops.
One requirement is that anything costing $250 or more be sent with signature confirmation of delivery. This either means that the buyer has to be home to accept delivery or take a trip to his post office. I did this once and had an angry buyer on my hands, luckily he calmed down and left positive feedback once I explained the reason to him - but the possibility of an angry buyer not wanting to join the seller in jumping through a paypal hoop isn't in the best interest of a seller. So I learned that if I believe the cost might be around or more than the $250 mark, I don't accept paypal.
Another requirement is that the seller must ship to the paypal confirmed address only. You must specify this in the auction's TOS (terms of sale) in order to require paypal buyers to have a confirmed address. You cannot block them from bidding on your item, but you can block them from paying for the auction through paypal.
This could give you another angry buyer if they didn't read the TOS, but they do have the option of having their paypal account address confirmed prior to paying. But if they did read the TOS and don't have a confirmed address and do not care to get one, then you have effectively only limited the bids you will get for your auction.
Along the same lines, confirmed addresses can be PO boxes. UPS cannot deliver to a PO box. There is no way to block a PO box confirmed address. So if I am going to ship the item UPS, I do not accept paypal for the auction - so as not to further limit my bidding pool... or find out after the auction that I can't meet the SPP requirement by having to ship to their street address.
And the requirement for confirmed address shipping can prevent a seller from honoring the wishes of the buyer, like the reason they won your auction in the first place. The best example I have of this is the mom in Tucson that bought my model T head as a present for her son in California. She asked if I could ship it to him. If I had taken paypal I would have had to say "No".
Just a few additional things to consider if you only want to pay with paypal.