I am UK based.
My first boards were contracted as 100 to a Chinese company and 100 to a UK company. At that time I had no idea what the demand was going to be. The board was about 1"x2" with 110 parts, mostly 0402, a sprinkling of SOT-23s and three fine pitch QFNs. The BOM was 30 line items, all but two of the parts on the top side with a crystal on the bottom and an edge connector that needed hand soldering. Otherwise it was all SMD.
For the UK manufacturer, I supplied PCBs and parts (aka "free issue"). They assured me they could do 0402. They had four weeks. The day they were due to deliver, despite interim asurances, they sent me about half a dozen boards hand soldered and my parts back, saying they couldn't do it. They were charging about $8 per board. Lesson one: never trust anyone in manufaturing based on cold calling.
The Chinese outfit insisted that they would supply the boards and parts, and assured me in writing that they would use the exact parts on the BOM, from the suppliers specified (eg, Farnell, Digikey etc). They also had four weeks to deliver, and they did. However there was a 50% failure rate because a dodgy 1.2v regulator they'd used dumped 5v onto the most expensive chip on the board, blowing that up too. They also had the brass neck to complain to me that a comnector didn't fit the board, well that's what happens when you don't buy the connector specified on the BoM. They charged $5 per board for assembly, and parts and PCB prices were on a par with what I paid anyway. Lesson two: my concept of an assurance is not the same as some others, there are fundamental cultural differences, although at the time I wasn't quite so charitable with my language.
Then the Chinese New Year hit, I was left with no domestic manufacturer, and one crap Chinese one with a minimum lead time of six weeks.
By this time, I realised that I had a hot product, each time I updated the inventory with another 100 or so it sold out in under a minute. I ended up hand placing amd reflowing nearly 200 units myself.
At this stage I was about to give up, I did not see my career as a human pick and place machine going anywhere.
Then out of the blue, I had a call from an assembler who'd been recommended to me about an hour's drive away, and who I'd asked to quote before but they were too busy at the time. I asked them when they could do 500 boards, "next week" was the answer, $12 per board, I supply PCB and parts. After biting their arm off, I jumped in my car to see them. After all, at this stage contract manufacturing to me seemed like a cowboy's convention. I pressed the flesh, saw the whites of their eyes, and with some trepidation left them with the parts for 500 boards that day. A week later, my boards turned up, all assembled and tested. That was four years ago, and I still use them for all my assembly, we have an excellent working relationship. Yes, they are 2.5 to 3 times more expensive than the Chinese guys, but I have peace of mind and don't have to employ someone to look after my interests overseas. And if there is ever a problem, like parts shortages, I can jump in my car and correct it within an hour.