If someone sends me money form Paypalme, can he or she refunds it?

[Kriis]

I'm selling a service online (a one-time thing), I don't want the other person to refunds his/her money after I'm done 

[kernowlass]

@Kriis 

Read up on Paypals seller protection policy so you can risk assess your transactions.
Legal (bottom right of Paypals pages) > user agreement > seller protection.