Used Clifton Cameras, Park Cameras, Mifsuds and Warehouse Express several times.
All very good service. Mifsuds have been very fast replying to email. I have a lens on order with them now.
All these companies have offered me the chance to cancel an order when they did not have the stock.
I have also bought from SRS Microsystems and they did not offer the chance to cancel the order when out of stock. They are entitled to do that, but it's not a customer friendly way to conduct business.