Is it true that the revenue department will visit every company every year? or only the first 3 years from the date of the start of the company?

how about customs department? do they visit?

Revenue department only dropped by once, about a month after registering for VAT.

Haven't seen them once afterward, but we are paying taxes on a regular base.

Customs is a different beast altogether!

Especially for factories for example bringing in parts (NOT imported), assembling whatever from it and then export the finished item. They every so often do very detailed stock checks, to make sure that none of the parts (on which no import tax has been paid) have made it into the Thai market! They either have to be in stock or exported. Massive fines if the count doesn't add up...