I fish every week during the summer and over the years, I have been stopped plenty of times by all the agencies, coast guard, dfg, border patrol, etc.
All my interactions have been professional and courteous.
It only seems that people with attitudes and/or have something to hide have negative contacts.
I'm glad they're out there making there presence known, when it comes to fishing, I see too many people not playing by the rules.
All the water agencies work together, Just a couple weeks ago, DFG stopped a boat for a check and found that they were smuggling people and turned them over to border patrol.
As far as I know dfg, coast guard, and border patrol do not need probable cause to board a vessel on navigatable waters.
Show them some respect and they will usually do the same for you.