Sure, that helps for distinguishing krzeslo vs fotel, but the problem is all of those items in fotel are also chairs, and I'd expect 'chair' to be used more commonly to refer to them than 'armchair'. There's also some in that series that don't have stuffed/upholstered arms, and so I wouldn't think of them as 'armchairs' at all.
Why is the original sentence "Nie sprzedajemy foteli" rather than "Nie sprzedajemy żadnego fotela"?
(I hope "żadnego" is the correct genitive here...)
I thought the general rule was "the more negations, the better".
EDIT: Corrected foteli to fotela as per ZosiaD5. My original question remains unanswered, though...