This is not about who is playing, what they are playing, of even if they should be playing an instrument. I will discuss that at another time. Let’s just talk about how an instrument is set up to make it as easy to play as possible. Let us trash the myth of ‘ an instrument has to have a high action to get lots of volume ‘.
Is the neck straight? This means are all the frets at the same height on a flat surface. Your instrument must have a flat fretboard to get the best playability from it. You can look down the neck to see if it is warped or twisted, but your eyes are not good enough to see if the neck is bowed down or humped up. To check for a flat neck you can use a straight edge ruler, or do as I do. I use the banjo strings. The best way to check if the neck is flat is to have all the strings on the banjo, with the strings being close to ‘in tune’ as possible. This puts the correct pressure on the neck. Now, with a finger, press down the middle string at the first fret. With your other hand, press down the same string behind the last fret. You are using the string as a straight edge guide. Check under that string at the 10th fret to see if there is a gap between the fret and the string. If the space between the fret and the string is more than the thickness of a sheet of paper, the neck is bowed down and needs to be adjusted for best playability. If the string touches the 10th fret before you have the string all the way down at the last fret, the neck is humped up and needs to be adjusted. Sometimes the neck gets out of adjustment because of high or low humidity, but most often because it was never set up correctly after it left the manufacturer.
This is the adjustable steel rod placed in the neck under the fretboard when the banjo was made. Without a truss rod, the banjo neck will bend until you can shoot arrows with it. (Another of the 1001 uses for a banjo.) A lot of pre-1920’s and cheaper banjos were made without an adjustable truss rod. You don’t want one, unless you want it for decoration.
How do you look for a truss rod in the neck ? A small metal or plastic cover plate on the front of the peghead is usually held on by two or three little screws. Under this cover plate will be the adjusting end of the truss rod. A nut or socket head can be tightened to straighten out the bowed down fretboard, or loosened to reduce the humped up fretboard. This adjusting is not recommended for inexperienced persons, because sometimes even 1/4 of a turn is too much. This info is given to you so you are aware that with a truss rod, the neck can be straightened. A banjo with a bent neck is not very playable past the 3rd fret.
Check the frets are the same height all along the fretboard. Check to see if the frets are all the same type and size. Someone may have replaced frets with fretwire that is skinnier or fatter than the other frets. Frets come is various widths and heights. Electric basses have very large fretwire, while mandolins have very small fretwire. Check the frets have no deep grooves in them under the strings. This will make the strings buzz on certain notes or the note will not sound clear. Really deep grooves cannot be filed out and need to have the fret replaced. Replacing frets is a professional level repair.
Check the tuning pegs will keep the strings in tune. Sometimes the screw on the bottom of the peg knob is loose. This screw should be fairly tight to prevent the peg from slipping. On the type of peg with a top nut and washer holding it on, make sure the nut is fairly tight to prevent it from turning in the peghole.
Check the tightness of the head. The bridge should not sink more than 1/16th of an inch below the head level. The easiest way is to look inside at the back of the banjo head. If the head is too loose, the bridge feet will make a big bump or sag in the head.
I will discuss head replacement and tightness in another article.
This is the actual height of the bridge. Bridges come in different heights such as 1/2 inch high to 3/4 inch high. The standard is 5/8 of an inch high. All adjustments should be made using the 5/8 bridge.