I have sold many items with 100% positive feedback and will only accept PayPal if it IS F/F. There are several reasons here.
1) PP never supports the seller if there is a dispute, and fraudulent buyers can lock up the money while they have your item.
2) Regular PP charges over 3% No need for this.
3) Regular PP generates a tax statement to the IRS and Seller. Even tough there is never a profit, the forms must be filed with your return I am not a business.
So don't discount sellers who only take F/F. It is not their fault. If you want absolute protection buy new or from a company with return policy. Talk to the seller. You can tell...