Is onward proof of travel always required at land crossings into Thailand?

For land border crossings, they'll pretty much never ask for proof of outbound travel. Even less so if you arrive by car or motorcycle.

Some obscure or "troublesome" nationalities may be asked.

Different country but just so you know, I traveled with my Chinese colleagues from Thailand into Malaysia (earlier, we came from China to Thailand via Laos and made a second entry into Laos and back).

At the Malaysian border (Bukit Kayu Hitam - Changloon, which is the busiest border crossing, the one with Sadao) I handed all passports through my car window to the officer.

I was stamped in immediately, but my colleagues were directed to another window and had to get out of the vehicle.

There they were questioned and asked to show their outbound flight tickets (which they had - a ticket to Indonesia departing 6 days later). They were told they'd be given a 6 day entry, matching the ticket (the official thus gave less than the 30 days they would have been entitled to under the e-visa). In the end, he stamped them in for 1 more day, a total of 7 days, in case of a flight delay or something. They were first time visitors to Malaysia.

I think in future, expect Thailand to do this kind of thing too.

Thailand just want to know, that the traveller is intending to leave Thailand again, within the mutual agreement made at the Immigration on arrival.

For land crossing, no one has ever asked me for my onwards ticket 👍

They always accepted that we were leaving by land and couldn't purchase a ticket yet

NO:

Dont forget , ur ONLY allowed 2 visa exempt land border crossings/calander year

Bus ticket is fine

Immigration very rarely ask. Generally it's airlines who want to see proof of onward journey before they allow you to board, so land crossings are ok, unless you've got a lot of history of visa free entries

Never been asked by air or land. You and always use bestonwardticket if you are worried