I used Smith and Hall (previously Galleries Direct) to purchase artwork under one of their guaranteed rental plans. They chased hard before the purchase but once I purchased, their customer service left a lot to be desired. During the rental period they missed two payments and didn't apologise or offer the additional interest owed under the agreement (admittedly only a dollar or two).
I also found by reviewing other artwork after my purchase that the price I paid was somewhere between 15% - 20% above market value.
They rarely return emails or phone calls, and although promising up front to keep me fully up-to-date on my artwork value with minimum yearly reviews, I have never received anything from them (4 years now) even when I have specifically followed up.
I would not recommend dealing with them if you are looking to invest in Art.