[Arran]

If he isn't a lowball offer type guy then he must have a price in mind for it. Without photos or knowing the electrical condition it's hard to pin down exactly what the set may be worth, but ordinary late 1920s consoles are not typically high dollar radios regardless of make. I have an idea of what I would pay, or at least the maximum I would pay, but it would depend on it's all around condition like whether it plays or not.
The model 531 apparently used the same seven tube chassis as the 511 series table sets, so that means a string of type #26 tubes and a a #71A output. What style of cabinet is this set in, a highboy or a lowboy? By the looks of things the model 86 version looks like a better buy in the lowboy cabinet since it would use an electrodynamic speaker instead of the old fashioned magnetic speaker, it also would use screen grid RF amplifier tubes like the type #24 and a pair of #71As in push-pull so it would be a better performer.
Regards
Arran