There is very little about this company online, but I haven't seen anything negative so far.
I would suggest you do valuations, and ask a local garage to come round to value your car, and also see if you could find out it's glasses guide price. Prepare yourself for any local dealers to haggle hard, and not give a good first (or even second) price.
You could try parkers online or what car, but in my opinion these always overprice what a car will be worth when you come to sell it, but should give it a ballpark figure.
When selling your car, make sure the payment clears your bank, and that you have seen identification from the purchaser, and have completed and retained the part of the registration document (V5 / Log book) - to make sure you are no longer liable for it. (Write the time on there too!)
Good luck with it.
Sparky.