Most 'anti scanner' laws are local, not statewide. They will vary from county to county, and city to city.
Your shops may have been burned by having something they installed confiscated, and they could never 'protect' against it, because you could drive from the city they're in, where it might be legal, to another a half mile away, where it isn't, and have trouble. If so, they just don't want the hassle.
Some examples, including rediculous but on the books ones:
Listening in Los Angeles
Southern California scanner listeners also have local laws to contend with. The City and County of Los Angeles both have ordinances dealing with scanners. In Los Angeles County a 1944 law still on the books makes it an infraction equip any vehicle with, or operate any vehicle equipped with, a short wave radio receiver. The ordinance defines a short wave radio receiver as any radio receiver or other device capable of receiving messages or communications transmitted on any radio transmission station operating on a frequency between 1600 kilocycles and 2500 kilocycles, or on a frequency between 30 megacycles and 40 megacycles, or between 150 megacycles and 160 megacycles.
Similarly, the City of Los Angeles in two local ordinances restricts the use of scanners within the city limits. First, SEC. 52.44 titled "Willfully listening to Police and Fire Departments portable radio messages prohibited" makes it unlawful for any person to willfully listen by means of any radio receiving device located in or upon any vehicle to any official message which is being transmitted by the Police Department or Fire Department of the City of Los Angeles or any law enforcement agency over a radio transmitting station owned or operated by such city or agency.
The City ordinance does not apply to persons to whom a permit to listen to such radio messages has been issued in writing by the Chief of Police of the City of Los Angeles. And those permits are completely discretionary, which means they may be issued after he determines that public interest will be served by the issuance of such permit but don’t have to be issued. The City law does not apply by its own language to any officer, agent, or servant of any government agency or public utility, the performance of whose duty as such officer, agent or servant, requires that he listen to such messages.