You go where the money is. IIRC, one client was William Shatner.
I have a small antique shop on Long Island (Moriches, NY). When customers ask me where I get my “stuff” I say, “I’d have to kill you if I told you!” They get the point!
And then go to the estate sales, right? 
Zyada and I go to estate sales pretty often (mostly just to look), and sometimes find great stuff. We decided long ago that garage sales are full of stuff people want to get rid of, but estate sales are full of stuff they wanted to keep.
I go to a lot of different types of auctions, estate sales and yard sales just to kill time and they all have their little quirks and groups of people who tend to follow them around. Dealers, collectors, pickers and just bored people with nothing else to do. Some times things go for almost nothing, sometimes people bid stuff up incredibly high.
I bought a room full of books for $50 once because the book buyers where out in the yard looking at other stuff when they sold the room; auctioneer didn’t get offers on several books so he just thru his hands up and said what will you give me for all the books. As I was cleaning out the room I sold about $400 dollars worth of books to people who showed up late and got the ones I wanted for nothing.
Another time an estate auction started while the relatives were still arguing with each other on what they were going to bid on and I bought three nice old Indian artifacts for cheap. Boy were they pissed and they tried to take them back from me. Auctioneer said he would call the sheriff on them if they continued to harass me and upset the auction process! You just never know what's going happen.Years ago I had a friend with a degrees in fine art. He made his living by scouring flea markets, auction, estate sales, etc for old art work. Meaning the kind you hang on walls. He had regular places to visit and spent almost every weekend going to auctions. His house was full of paintings, art books, auction circulars, and antique magazines.
He told me most of what he bought and sold was pedestrian and he only made a few hundred dollars per painting. But, but…once every 12-16 months he came across the find that would make all his work worthwhile. Those painting he would have cleaned up, take to NYC and get to a gallery or auction house to resell.
I know he did exceptionally well. This was on the coast of New England so plenty of old families with old houses to clean out when things passed down. This was long before Antique Roadshow and other such programs, so I not sure if he could do it now, or not.
A slight twist, I do some antique refinishing as a side part of our metal working shop. I’ll buy an old beat up item cheap wherever I find it, restore it, and make a few dollars after my time and effort is added in. A nice little income stream when things are slow in the primary buisness.
I love house liquidation auctions. Buy a whole box of stuff, sell one or two items and make the original purchase price back. Then everything left is profit if sold or pieces and parts I can cannibalize for other stuff. Not intrinsic value in parts, but worth their weight in gold when a customer brings me an item with a broken or missing part.
If anything ever happens to me and my partner in the shop, the kids will look around and be clueless at the “junk” squirrled away in the nooks and crannies and probably haul it off for scrap!
That reminds me of two stories. A few people in the area do similar work. We all more or less know each other and will refer people to each other if they are more approprate for that job. Frendly competition when our skills don’t overlap. Anyways, one older guy died, his son offered us the contents of his shop. Hell yes we thought, the son then quoted us thousands of dollars, um- hell no. It was absurdly high. Same story earlier this year. This guys son said Dad always like you, take it all, save me the trouble. We gave him a few hundred dollars to ease our guilt over feeling like grave robbers.
People are odd when it comes to old stuff and money. I seem to see the either/or of percieved value of $5 or $500, rarely the middle ground.
I enjoy antiquing, especially when I am on vacation. I often prefer to stop at antiques store in smaller towns.I like to think that whatever I buy has been there for decades. But is that true? How likely is it that a vintage postcard or toy soldier that I buy in Dodge City, Kansas (or somewhere like it) has spent it’s entire existence in that area? Was it most likely owned by someone in that town, state, or region? Or could it have come from anywhere in the country? Would the answer be different for something I bought in a large city instead of a small town? Would it vary depending on the item’s value?
How do you become a picker? Are most pickers independent entrepreneurs who roam free and independently and have a little book of contact details for antique dealers that they suspect might be interested in stuff that they might find (and who might end up holding the bag if they can’t get any actual vendors to buy the stuff they found), or can one reasonably “sign on” as a picker with some dealer or network of dealers and earn a wage or salary? If you can “get a job” so to speak, what’s the career path? Is it haphazard and without standards or are there certifications to earn and whatnot? E.g. a Certified Apprentice Picker passed a test indicating that he knows the difference between a folio and a quarto and knows generally where to look for manufacturer’s markings on china, but a Master Certified Expert Picker can spot the difference between a 1810’s Boston desk and a 1790’s New York desk at 100 meters in the dim light of dawn.