Rubbish, in fact. Incorrect keys, totally wrong positions/fingerings, etc.
In other words, hacks writing for hacks. Let's face it - 80% of rock/pop tunes shouldn't require any written notation with their I/IV/V progressions and easy-to-pick-up-by-ear arrangements.
Many publishers of instructional DVDs have been dodging the copyright laws for years with titles like "In The Style Of The Eagles" - all the greatest hits are presented in 10-second bites with album/song titles cleverly omitted even though the passages are played to mimic the records. Perhaps the authors/distributors hope to hide behind fair use.
The sheet music industry are even more technophobic than the RIAA however - they still want to sell actual sheets! PDFs would sell like hotcakes and despite any threat from end-user copying it would almost certainly replace the lost revenue from hard-copy sales.
I rarely look at sheet music but I seem to recall single songs priced in excess of $10.00. Once again, an entire industry segment fails basic economics.
Sheet music has been bootlegged since day one.
And in the 1800s it could cost 50cents or more for a song. Figure out that in modern currency.
Steely Dan proved just how bad tabs are. When they reformed for the Citizen tour neither Don or Walter could find their original sheets so they went out and bought a bunch of tabs, started playing them and got a definite “that ain’t right” feeling, wrong rhythms wrong keys wrong everything. So then they went and got copies of the albums and did their own tabbing.