just turn up and present your passport, don't say anything unless asked. They may ask about if you have ticket to leave Thailand that's about it. Do not ask if you need a visa as you don't, asking may just only lighten your wallet for no reason.
I helped a friend do his and was done in 4mins the payment processing took longer than applying. But yeah if you not familiar with the layout and what visa you need to apply for I can see it being a pain in the ass to negotiate for some people
its the people where they issue the drivers license thar won't except the letter. I also said I would definitely stay 2 months not 3. I've offered them the 1000baht to negate the discount given but they not interested in that. The issue is lack of tm30.