Given the task definition and input, reply with output. Given a travel related situation, and given a specific question about the situation, summarize the question into a title

I've read the border between Thailand and Cambodia was difficult to cross for foreigners.

What's the best way to cross that border for foreigners ? Is taking a flight mandatory or is there other solutions ? And what would be the cost of the crossing ?

EDIT : I was hoping there was some preferred path to go from Vietnam to Cambodia. Let's say I want to leave from Bangkok to go to Siem reap.

What is safe for me ? Something that does not look like this thread

What is cheap ? Everything will be cheaper than what I'm use to. I want to know the cheapest path that is relatively safe. Crossing the border illegally is obviously not an option.
What is the cheapest and safest way from Thailand to Cambodia?