Give them a ring and sound them out - ask for references of satisfied customers.
They should give details of the 'real' institution or person behind the trading name on the website. I believe it's a requirement of section 4 of the business names act 2005.
If they are a company then the 2006 companies act requires all UK companies to publish certain details:
The First Company Law Amendment Directive came in on 1 January 2007, and you're now required to put the following information on your website and business emails:
* Company registration number
* Place of registration
* Registered office address
You're also required to have the following information on your website:
* The name, postal address and email address of the website's service provider.
* The name of any trade bodies or professional associations that the business is part of, including membership or registration details.
* Your VAT number, even if the website is not being used for e-commerce transactions.
* Any prices on the website must clearly state whether they are inclusive or exclusive of tax and delivery costs .
Personally I think the 'from' prices will only be the start!
Let buyer beware as they say...