You are correct in that there is no one way that an in law will get described in a listing. You are best off finding an agent you like who regularly works the area in which you want to purchase. It doesn't cost you anything. There are profiles of agents on this Site, zillow, yelp etc.
If you want a detached studio in Berkeley, more likely than not itâ€™s going to be a converted garage. Again, your Realtor can search for you by searching the MLS for key words like â€œstudio, unit, in-law, law, mother, converted, legalâ€ and so on. A quick search revealed 5 properties that responded to these key words. One of them stated, â€œ2/1 unit attached to the house, permits unknown.â€ Thatâ€™s usually code for â€œillegal.â€