Fret Markers
Instruments- discuss specific features, luthiers, instrument problems & questions
One word of caution to those who use stickers on their fretboards-
There are good products for removing sticker residue once you've decided to remove longtime stickers. However, few people take into account that wood darkens over time when exposed to light- even normal room light while playing. If you leave stickers on for a year or more, when you remove them you may find that the wood is lighter colored under the stickers, thus you are left with unsightly 'ghost' marks where the stickers used to be. These marks don't even disappear when you rub oil on. I've seen these poor dulcimers on Ebay with their ugly light colored rectangles up and down their fretboards. So, consider removing fret board stickers after your initial learning period, before they create permanent cosmetic damage.

Still, you have done him a favor because future clients will have a hard time with his strangely placed fret markers as well, if he doesn't understand a diatonic scale with its half and whole steps and how they are used in tuning and playing.