"What is my guitar (or mandolin, bass, banjo, amp, dobro, etc.) worth?"

Best periods for Gibson and Martin and why.

On the banjo, there will be a “stick” that bisects the pot, connected to the neck. There is no stamping anywhere on that?

They made tons of them in the teens as nearly every town had a ‘mandolin orchestra.’ It was a huge fad that lasted about 15 years and gibson sold ‘em the instruments AND the lessons. When the fad died off, they assigned their best engineer to revive people’s interest, and the engineer (Lloyd Loar) tried to do that by redesigning the mandolins to be better instruments. He was successful at that, but not in reviving the fad! Gibson mandos made after the Loar period (’22-24) are much better instruments and also more rare since people stopped buying mandos and Gibson moved on to other pursuits, mainly 4 string banjos. My mando, I can proudly say, is a Loar era. Yay for me.

How to judge the condition of a vintage guitar: If it passes the dime test, (see video above) it likely doesn't need a neck reset and the action is good.

Next, hold down heaviest string at 12th and first frets and look at gap between bottom of string and top of sixth fret with your string acting as a straight edge. Should be a tiny gap, like a business card height. This is the test is to measure neck straightness. Do the same thing with the highest string. The gap should match the gap of the lower string. If the gaps don't match the neck is likely twisted and that is hard to fix.

Holes in top, jack holes, input jack, strap button (on headstock!)

Many guitars (mainly Gibsons, since they invented and patented it) have a truss rod in the neck which, if functional, can help correct a bow, adding or taking away relief.

Next, take a piece of magazine paper and try to slide the corner under the bridge edge on the side opposite the strings. Often it is surprising how much of the paper will go under, and indicates the bridge is lifting and will likely need to be removed and re-glued. This is about a $200 job. If not repiared the bridge could eventually fly off and take some of the top wood with it.

Behind the bridge there is likely some "belly" in the top , where the top is swelled or risen. This could be a sign of loose bracing or just the natural body distortion caused by years of string tension. If it is not loose bracing it is not repairable and the guitar's value should be considered with this in mind.

Look in the sheen of sun for cracks. Cracks are always straight lines with the grain. They usually emerge from the edges of the pick guard or from the bridge towards the butt of the guitar. If it is straight line coming off the bridge, it is NOT a finish crack. Finish checking (loose spiderwebing or broken glass or grid looking) is normal and almost desirable as it indicates that the finish is original. Cracks are not not deal breaker but about $100 each to fix. Cracks in neck or headstock are dealbusters. Is the bridge plate original and in good shape? This requires an inspection mirror or a camera phone slid between the strings and pointing up at the underside of the bridge. Original Martin bridgeplates are almost always maple and 1 to 1.5" wide. On older Martins the bridge plate is tucked under the X-braces at either end. Gibsons bridgeplates are often bolded in but never tucked. A replaced bridge plate on an old guitar can harshly discount an instrument as this area is the most key area for sound/vibration transfer. Also a replaced plate could indicate top damage beneath it. Large bridge plates are tone-killers, as well as value killers.

They would often take a mandolin that someone was done with, return it to the factory where it was re-finished, and then sell it again as new! And they made bank selling lessons and sheet music.