You can paint over flyspots but they tend to burn right back through to the surface! I know of people that painted over them THREE times and they still came through!!
Because ply poo is very acidic. If you consider the way they eat it’s hardly surprising: a fly eats by landing on food, vomiting on the food which liquifies the food and then sucks the liquid up with it’s probiscis. Its faeces is obviously VERY acidic as well.
So when you paint over fly poo it just burns through the new paint making its appearance a few hours later. Very confusing and frustrating for the homeowner who spent a loooong time painting their ceiling!
I hope you were not eating a meal with flies buzzing around as you read this!
The solution, of course, is to clean ALL the fly poo off before even thinking of painting.
If it is professionally cleaned you may decide it looks so good it doesn’t need painting anymore.