This is certainly a pet peeve . Particularly in California, where it is I believe not legal or at least uncouth to sell produce at a farmers market stand not grown by the that Farm.
I can't say it has gotten better over the years , but some booths are excellent and some are not. Find your favorites and go from there. Murray family farms is the gold standard I have seen in CA .
Kashiwase and Frog Hollow stand out to me for 10+ varieties of named stone fruits in season. Many places you ask what kind of Peach or Nectarine they say "White". I would not make a good poker player as the look of disdain is surely noticeable, (suck teeth)..
Brokaw is always good with their named Avocado varieties but I learned they spray poison so that sucks.
Hawaii you almost don't bother , they look at you like your crazy , I look at them like they are crazy. There are some farmers that rep only what they grow, but that is the minority and doesn't exist at all at the 2 biggest markets .
One major issue is there is a ton of stolen produce sold by thieves or middlemen without any regulation or inspection, the farmers market booths have no idea and all have the same standard response when asked what cultivar "very sweet" .( incredibly annoying for Durian in particular) 2. You can see the Costco boxes of Mango, Pineapple and somehow even Banana sometimes sitting behind the booth, no shame or even idea of why that's wrong. They are just hustling hard .
I will always gravitate towards a farmer selling their goods they grew at market . These are my hero's and folks I can usually relate to well.