If you’re in business and you want to be paid for some goods or services you have supplied, you need to issue a document called an invoice. This will provide details of your business, what you have supplied, the amount, any other charges, and any Value Added Tax. The bottom line of this invoice will show what you are owed.

 
If you inherit a stamp collection and sell it on eBay as a one-off transaction, then no tax is likely to be payable. There might be a theoretical charge to Capital Gains Tax, but in practice this is a relatively lenient tax and often the charge turns out to be nothing. However, if you make a habit of buying stamps as and when you can and selling them online, then you are now engaged in a trade and your profits are chargeable to Income Tax.