If in the UK., there's a visa email you can contact and I'm sure they'd advise you whether they'll accept a one-way ticket, if you explain that with your sixty day visa your applying for you'd like to get a thirty day extension whilst in Thailand. Personally I've flown into Thailand dozens of times on one-way tickets and without a visa and got visa exempt thirty days, although this was many years ago.
The proof I was seeking was assuming this was about setting up a Ltd., company with six Thai partners, plus one farang to purchase a property, so the only investor, the farang could protect his investment. If the Thai Government as I've said previously let foreigners buy houses, but put restrictions on how they could sell them, instead of them being able to speculate for profit purposes, then that'd we'd out genuine foreigners from those who'd like to abuse, by buying cheap & selling at a profit.
I went to immigration many years ago, as my visa was about to expire. I had a bad dose of food poisoning and told the IO., I was too ill to travel. She said she could give me a 15 day extension for 1,900 baht
Be careful, the Thai tax will be after your hard earned savings if you stay more than 179 days in Thailand in any year, 1st of January to 31 of December.
And still the billionaires and multi National companies will get away with paying little or no tax. As usual the ordinary guy/girls will be taxed to the hilt.