Unfortunately not.
Most merchants will display the PayPal Logo or the PayPal Verified Seal if they accept PayPal. If you see the PayPal Verified Seal, click on it. You will then be taken to the PayPal Login Screen whereas you then login with your account info. After that, some info will be displayed about the merchant. Note, the info is limited, you will see their email address, their account Status (should say Verified) and the date they created their PayPal Account. Understand that PayPal's verification system does not constitute an endorsement of a member, nor a guarantee of a member's business practices.
Else your option would be to ask the the merchant in question directly.
PayPal does have a commercial Store Directory however, that's not a complete listing of all the current Merchants who accept PayPal.
https://shopping.paypal.com/stores/?conversationId=1718493
