The last step of any guitar setup applies only to electric guitars with adjustable pickups. That is to adjust the pickup heights so the volumes will be consistent.
This is attained by moving the pickups either closer to or away from the strings, and therefore either more within or outside of the magnetic field of the pickup itself. The closer the string vibration is to the magnetic field of the pickup, the louder it will be, and vice versa. Almost all pickup manufacturers have specs that note the appropriate pickup heights. But as a rule of thumb, you will want the treble side a little closer to the strings than the bass side, as the string vibrations of the bass strings will have more side-to-side travel when played.
To measure pickup heights, you will simply suppress the final fret and then read the distance between the top of the pickup’s pole pieces and the bottom of the string. You can measure this space with a six-inch ruler and use 4/32” on the low E string and 3/32” on the high E string as a starting point. However, it’s a good idea to refer back to manufacturer guidelines for reference. Also, keep in mind that pickup heights can be very subjective and that you are definitely not testing the guitar on the same amp as what the customer is using. It’s always a good idea to ask the customer if it’s OK to make adjustments if they are already in the ballpark.