Have used them in the past as a last resort. Very expensive for collectible stuff but when all over avenues have been exhausted - internet, Ebay, Record fairs, etc - they usually have it. Gradings are fairly accurate as well.
Every now and then. As already said they are pricey but well establised and are very professional.
Last thing I bought from them a couple of months ago was a vinyl album by Forest which I was struggling to find elsewhere and they had a copy. Came swiftly and well packaged.
Yes I should have mentioned they have a reputation for being expensive for collectible stuff. I've only ever bought new stuff from them on which they are competitively priced.
If you aren't looking for collector's stuff I suggest you try: