So your suppliers can change the price of a pre-order you have already placed with said supplier on behalf of a customer?
Yes we buy in USD and that prices stays same but if we pay $600 for something and we set our prices using a 1.45 rate our cost is £413, but if rate drops a lot to say 1.30 our new cost is £461 so a near £50 increase excluding vat.
So web prices would go up, those who pre-ordered get the original price however.

