Notorious: My Celtic CD--listen & buy!
The Priest and the Publicans: Gospel bluegrass out of the box.
Emando.com: More than you wanted to know.
Donaldson • Rigel • Thormahlen • Andersen • Old Wave • Bacorn • Yanuziello • Fender • National • Gibson • Roberts • Franke • Fuchs • Aceto • Three Hungry Pit Bulls
They may not be as similar as it seems: Washburn switched its production from Japan to Korea in around 1990 and from looking at these two instruments, I suspect that the one in Denver is one of the earliest Korean ones and the one in Seattle one of the last Japanese ones.
For what it's worth, I have a 1989 M3-SW which looks quite markedly different from the 1990 M4-SW in Denver, in particular in the headstock overlay and the shape of the truss rod cover. The photos of the 1988 one aren't good enough to tell, but I think it looks rather more like mine (except I have a darker stain, with a light brown centre to the sunburst rather than orange). I believe mine is a late Japanese one; it certainly plays and sounds very nice indeed and has excellent workmanship. My serial number is eight-digit -- the 1990 one in Denver has a four-digit number. Of course, Washburn may have had a different numbering scheme for the M3 than for the M4, but an alternative explanation might be that they changed numbering scheme when they moved factories.
Those Japanese Washburns were very nice, with the Koreans having a less good reputation. However, even with all that, I would think that the Seattle one is considerably overpriced -- one can get way better mandolins for that money. The $550 for the Denver one is about what I paid for mine four years ago, and I think I got a very good deal.
Edit: Checking those online Washburn price lists, I see that the M4 listed at more than twice as much as the M3 in 1988, 1989 and 1990. This puzzles me, as I was under the impression that they were pretty similar in specs and quality. Not sure whether any of that premium still applies to the used market. I also see that my finish isn't listed as one of the standard options for the M3; maybe mine was a custom model.