How to pay for digital art via Paypal.

I've had a lot of trouble lately, and there's a lot of disagreement on how people should/should not pay for art. Admittedly, I'm not super knowledgable on paypal and I've never had experience with fraud like others seem to have.
This is just a super quick tutorial I'm whipping up because I've had problems with people paying as if I need to ship them items- which... I won't be doing, since I'm a digital only kind of gal. 
If anyone has recommendations/suggestions/critiques, etc. feel free to just comment.

It's been brought to my attention that Paypal will hold accounts if "deviantart" or "commissions" are mentioned in the notes. So for future reference- I'd just put ONLY your username in the notes. for example: "from Kennadee".
_{The above was an issue during the time period when this tutorial was first published. So far as I'm aware this isn't still an issue, but I generally keep it short and sweet when sending payments.}

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If you're a business and you're looking to SEND AN INVOICE to a client, this is a great tutorial: