These are fairly common as yours is about the third such request I have received over this past year about the same chair. Interest in Westnofa furniture seem to be increasing. From information that I have seen they possibly were a Norwegian export company. I believe the current Ekornes company either made items for them or purchased the company, or perhaps both. There seems to be a bit of conflicting/unclear info on that.
In either case these chairs are appealing to many collectors and you should have no difficulty selling them. Having the ottomans is a plus. I would estimate a similar value to what they are being offered for on the link you provided...maybe $850-1100 for chair with ottoman assuming they are in excellent condition with no need of new upholstery.
Expect about half of a retail value if selling to a dealer. You may want to try posting a free ad first to see if you have success on your own, however.
Barry Bryant GOMOD.COM :: bringing modern design home
