in many cases these are brand new guitars, just have no warranty.
Yes, i say this is correct, and sometimes there is a "2nd" stamp above the unchanged serial #. Truth be told some of the best values out there are on "B" stock Guitars if you can find them. Others should be along with their experiences and opinions shortly to compare. I am sure there are plenty of exceptions. This is just my opinion and what I have seen in the market as of late. The First run model sold for $1799+ shipping and the "B" stock model sold for $1250+ shipping within 2 days of each other. One was marked "B" stock with a small finish defect on the binding and the other was a First run F50 used with no defects. Here recently their wF50's listed on Ebay. On the used market I have seen "B" stock Guitars sell for anywhere from 50%-75% of the used price of a first run guitar of the same model in the same condition. If it is something that you can't even see or a small finish defect Dealers normally sell them new for somewhere around their actual dealer cost which is normally 50%-60% of Retail. Depending on the reasoning for the "B" stock label really determines what they sell for. Some "B" stock Guitars have actually sold from the factory with a limited warranty but most are sold with no warranty at all.
Normally "B" stock guitars retain their original Serial Number and only have a small stamp or mark on the label to signify that it is a "B" stock with no markings on the body of the guitar itself. In My opinion a "B" stock guitar is one that either had minor imperfection in it or was sold as a liquidation guitar such as Fender did with a lot of Guilds when they sold the company to Cordoba.
This is the same markdown that any retailer like Guitar Center and others would apply to that specific guitar on trade in. As far as those are concerned I usually price them at 50% of what a First run guitar of the same model is selling for in Good Used condition. I consider a Guild that has the serial number changed and the word "USED" or "SECOND" stamped in to the back of the headstock a factory second or "Refurbished" guitar.
I think there is a big misconception between "B" stock Guitars and Factory Seconds.