Critical points when painting/coating (interior and/or exterior)

Hello everyone,

I am currently researching on behalf of someone about particularly tricky topics in painting or varnishing, about which manufacturers tend to be reserved and do not want to provide information.

So to all the professionals here: What are such points where you would like to have more information from the manufacturers?

An example from a well-known planner regarding facades is that there are often no processing instructions from ETICS for window sills, and this has caused him difficulties several times.

What topics and tricky points are there in this area that cause you difficulties?

PS: I am not an expert, so please formulate as simply as possible