When purchasing from the Web, one of the things to prevent getting mislead by Companies claiming to be something that there not, or even companies claiming to be somewhere there not, like UK for instance is to check with Companies House and see if the company is registered and trading.
Also a clean website with a company address and more important a contact number to call if you need to speak with someone.
Its always an idea if possable to look for a website offering a showroom or sometihng open to the public, if possable drop in. An appointment maybe required in some cases.
Look at referances, check the internet for Reviews, Customer servays and more important customer comments. Google is a very good saurce to checout the company you aim to purchase from.
IF IN DOU'T, CALL SOMEONE, speak with a member of staff. let them know your intentions, stock, fitting or install, aditional costs if any.... Get as much information as you can, a little reasurch goes a long way.