The vast majority of guitars and basses have position markers on the fingerboard as a quick visual orientation, but for some reason people think this is a “crutch” of some sort on a fretless, which is utter nonsense. Having fret lines is zerobetween notes, and a huge aid in accurate intonation, particularly above the 12th fret, where the difference between in and out of tune gets progressively more incremental. The Precision Bass was named that by Leo Fender because the notes could be fretted with “Precision”, while any fretless instrument is always at best a close approximation of perfect intonation. The better the player, the better the intonation, but everyone has had the experience of hearing upright bassists who are slightly out of tune, and it’s accepted as normal. With years of practice, the same level of rigor required to achieve the “muscle memory” classical stringed players achieve is fully possible, but if fretless isn’t your primary instrument, and you prefer playing in tune, get a lined FB, like those notable crappy lined fretless slackers, Jaco Pastorius and Mark Egan, to name two.