I did express my surprise and ask if they were cheating me, all with a laugh and smile... hopefully next time I will be using an immigration office in another province 🤣
FYI Samut Prakan immigration charged me 500 THB for the certificate. They asked me whether it was for car or bike, and I naively said both. Total fee 1000 THB from immigration as they needed to give me 2 certificates! Cheaper than a uk embassy letter though.
The Land Transport office were quite happy with a single letter plus a copy, so I have a spare original to remind me how effectively government offices work. This was for a renewal btw last November.