This thread is almost 6 years old!
Your profit will be the VAT exclusive selling price less the VAT exclusive purchase price.
You pay the VAT on the selling price, less the VAT on the purchase price, to Revenue.
So if you sell item x at £100 plus VAT of 20% (total £120) and you buy it for £50 plus VAT at 20% (total £60), your profit will be £50 (100-50).
Your buyer pays you £120. You pay your supplier £60. You pay Revenue (£20-£10) £10.
The cash flows like this:
Cash from sale 120
Paid to supplier (60)
Paid to Revenue(10)
Left in your pocket - £50.
This is fairly basic so if you can't grasp this you really need to seek professional advice.
BTW: this is an Irish website.