As great as undercover detectives Starsky and Hutch are, there is no way they could cut, style, color and perm hair in a high end salon, and convincingly get away with it, unless they had many years experience in the hair industry. According to their back stories S and H have been cops for many years.
When Starsky sings "Auprès de ma blonde", instead of singing the correct lyrics, "Qu'il fait bon", he changes them to "il fait beau". While it is ok to remove the "QU", he has changed the correct lyric "bon" (good) for "beau" (beautiful). This is probably because the French sound "ON" is nasal, and near impossible to properly pronounce by a native American. Since he was undercover, he would have given himself away as a non-Frenchman---if his female partner had more than a passing knowledge of French, that is. Note: it is also grammatically proper to say "il fait beau" (it's lovely outside).
Starsky's undercover name is Tyrone but and is supposed to be French, as he does an accent, but French people aren't called "Tyrone". (The same would happen 5 years later in another Aaron Spelling show and another Mr. Tyrone, in Charlie's Angels Homes $weet Homes.) It is unclear who---in both instances---figured that "Tyrone" would be valid as a French name. They were wrong.
In the very first scene, Hutch is arguing with the beauty salon owner. She says the only reason I let you work here is because of civil duty. She should have said civic duty.