Yeah, my strategy developed years ago into taking interest lists, and using that to place orders that I front the cash for, and then I don't take any money until the product is actually ready.
It does mean the flakes leave me holding product, but it's much better than sitting on people's money. As long as it's just an 'interest list' and they haven't paid me a dime then they have no real stake to demand anything. You're so right, once people buy something suddenly their attitude can really change on you.
Here's the thing I would say to anyone doing hobby production, mods or repros or whatever else: it's cool to give back to the hobby. It's great to be a chill person just doing it for the love. But ... my advice is make sure you're marking up your product and not being shy about making a profit. You deserve it for your time, and it will keep you from burning out and ultimately able to keep doing cool stuff in the future.
Because this stuff is work. Dealing with customers and shipping and all the BS *after* you've done all the actual work to create the product alone kinda sucks sometimes. And the work you did to make the product is super real too. And it really can burn you out, even if it's also fun.
The money is nice, you can use it to buy more things for the hobby. You can use it to develop your next idea. And, it means that half way through your sales you break even, and the flakes leaving you sitting on something that might take a while to sell don't stress you out, because you're at least not losing money on them and in the hole.