If he Doesn’t buy a visa get will get another 30 day visa free exemption stamp which he can extend at his local immigration office for ฿1,900 for a duration of 30 days giving him a total of 60 days in country…
you get 2 land border crossings per calendar year (01 Jan- 31 Dec) and there is no official limit of arrivals by air but eventually you will run into an overzealous immigration officer that says otherwise….
if he purchases a visa in Cambodia let’s say a 60 day SETV for ฿1,900 at the Thai embassy/consulate he will be stamped in for 60 days which he can extend at his local immigration office for a cost of ฿1,900 for a duration of 30 days giving him 90 days in country…
With the visa he will not be charged one of his 2 land border crossings per calendar year (01 Jan - 31 Dec)