I know of one guy who does this with rafters, he shows up at the Oasis with vans full of kids all Summer and says he's taking "some friends" out for some fun.
ALL driftboat guides will have a square sticker that varies in color each year that says OR guide/outfitter AND Deschutes guides must have a BLM number or series of letters that are registered with the BLM, some will just be the initials of the guide or the shop they work out of.
When a guide goes out for fun he is required to cover up all guide info or fly a yellow flag from the boat. The BLM and OSP occasionally will record the info/date when they a see a boat on the water with clients and see if that matches up with the report filed by the guide concerning what days they were guiding that season.
The tougher ones to spot are the boats that just look like any other boat and there are certain things to look for. It becomes fairly obvious after a period of observation.
Authorities have been known to stop a boat, separate everyone and see if they get the same story from every person in the boat.
I actually had this happen to me many years ago. I had bought a boat from a former Deschutes guide and was spending a lot of time learning to row and fish spots on the Pine Tree float. The boat was highly identifiable due to it's unusual color. On one nice day I had a friend from work and his son with me and got questioned when we stopped for lunch at Jones Canyon. We had one OSP and two BLM folk drill us for about 5 minutes. It all turned out OK obviously, there was no monkey business going on. I repainted the boat shortly thereafter.
Anyways, if you do book a trip, do it through a reputable guide. Some guides are outfitters and have several guides working under them as do the FF'ing shops. Ask questions and look for the stickers and BLM info. ASK for their guide card if you are suspicious.