How do I get a receipt supplied with the product that I'm buying?

[bigbrickshop]

If you paid with PayPal you will have received a payment receipt email.

If your purchase is business related and you need a Tax Invoice for GST purposes and the seller is registered for GST they will either email or enclose an invoice. If they don't, you can ask them to email you one.

[2106greencat]

eBay purchase notification and as bricks has said paypal receipt is all you should need