I don't think the issue is that people are hiding the fact that their WFH situation is not ideal. The people who have crappy WFH setups are quick to tell everyone. They aren't trying to get away with working from home, they are asking to work from an office.
Even if you have this WFH certification like you talk about, that isn't going to tell your employer much. Some people will have great WFH setups and not be very productive, some people will have bad setups and do great work. The only way to see which is which is to observe their productivity. Certification won't help.