What are the rules for re-entering Thailand with a multiple-entry visa?

Any multiple visa issued by an embassy or outside Thailand is always suggested that the visa holder leave Thailand before the visa stamp expires and then return to Thailand within the next two days or more.

I do not advocate doing the extension inside Thailand because they will require an abundance of paperwork and financial proof.

Unless you apply for a visa in Thailand, you will be able to stay until the expiration date. Then you must apply for a fresh start visa again. There are no single or multiple entries unless you pay the re-entry charge. The scary thing is that there are so many paperwork required (if you do not plan to use an agent) and 3 sets.

Multiple visas from the embassy are much preferable. When your visa is about to expire ... simply exit and return to Thailand; you will receive an additional days.