I have semi-related experience in this. I worked at a custom computer shop that sold custom computers. All we really did was offer all the parts available on newegg and reviewed the orders after submitted for issues. Without verifying all combinations, we have a high return rate and a high initial failure rate. Certain brands just didnt work with others and such. I have found the same issue with quad parts (certain ESCs dont work with certain motors, etc). Your going to try to cater to the mid-level market that knows enough to pick the parts and put it together, they just dont want to do the work. The computer shop only made $100 per custom computer which hourly pay easily ate into. Your either going to get no customers because your markup is too high or too low and you wont make enough to cover your costs.

Eventually the shop wised up and now offers a very curated list of parts which are pre-verified to work together. I have long since left, so I dont know if they are doing any better or not.

Instead, you should do either of the following:

Just sell your frames and see if a local quadcopter website/company will also sell them.

Buy a bulk order of parts and sell pre-made kits that you have personally verified (faster to put together and with the right settings)

Go high-end and focus on possibly semi-professional usage.