@Harry *******
You don’t need to pay anything to an agency — you can easily handle the process yourself. The safest and cheapest way is to apply for a Non-O Retirement Visa from outside Thailand (preferably your home country). Once you arrive in Thailand with the Non-O visa, everything is straightforward. You can then convert it to a 1-year retirement extension without any problems.
Doing it yourself means no unnecessary agency fees and no risk of agents overcharging or pressuring you in the future. The process is simple if you follow the official requirements.