Will I be asked for forward travel when crossing into Thailand at the Trat border, and is it a good crossing?

I've crossed that border, not for a border run though. And I wouldn't call it a "good" crossing, it's very old fashioned, slow and laid back. Not very clear what is where with signage, at least in English.

So a bit of an adventure.

Note that you can only do a land border visa run 2 times a year in Thailand.

Officials just sit inside behind the glass service desk while some Cambodian hustlers will help you for a small tip, nothing to worry about, I paid 20 TBH when he asked for a tip at the Cambodian border.

The forward travel question at the airport depends on your passport and any other thing they may have doubts about. So I'm guessing here as well.

Having a European passport myself, I've never been asked that in Thailand and neither at this land border.

Also this is a known land border for visa runs.

When I crossed over to Cambodia there were 2 guys from US that went straight back in to Thailand, which they've done before.