I travel back and forth in and out of Thailand every 4-6 weeks and sometimes stay for upto ten weeks at a time. I never ever have any issues with Thai immigration. I went to Vietnam for a week over Christmas and was asked how long I would be staying this time, I said maybe two weeks and they gave me 45 days as usual.
I fly in and out every 4-6 weeks and never have any issues. Occasionally they ask how long I am staying but never ask to see any outward ticket. I have never overstayed so I think they “trust” me. I have a friend who gets roasted every time he comes in, presumably he has a red mark by his name.
I could well be wrong, but I thought you didn’t have to buy a ticket before getting the visa? What happens if they decline your visa? I thought they actually advised you on the website not to purchase a ticket?