if you are serious about getting into bitcoin trading, stop using paypal for your bitcoin-related payments. paypal transactions are reversible, bitcoin transactions are not. I am sure you can see the problem here...
you can also make them add in the NOTE that they will not chargeback or dispute the transaction as this is a sell of virtual goods and that they have received them and that they are 100% happy with them and can't change there mind as sale is final
It doesn't matter what you put in the NOTE section, and the "all sale is final" doesn't work either.
PayPal will reverse the transaction, and even eat the money themselves.
I've used paypal for about 5 years with tons of transactions reversed with no good reason. Just avoid paypal, period.