If you haven’t been through Poipet before then it works as follows.
When you get to the Thai Immigration side there will most likely be a very long queue for exit, it will be ninety-nine% Thai and Cambodians waiting to go through.
Don’t join that queue. Atthe authentic Imm’ departure side they go through on the ground floor and you go to the stairs that lead to the upper floor, it’s generally a much shorter queue.
Stamp out and go through the exit. Walk across the bridge and you will/might see people, expats, queuing outside a building on your right. They are getting their visas there, you don’t need to, you have yours already ( e-visa ).
Keep walking and just ignore the we can help you with visa sir merchants.
After about about 300 metres you’ll see the ‘enter Cambo queue’ right hand side of the road after the Casinos.
Make sure you have a pen to fill out the landing cards etc, not easy when all you have is your knee as a desk sometimes.
I always made two copies of the e visa, one to hand over and one for return to Thailand, I know it’s not really required but when you return it helps the Cambo leaving side as they will spend ages flicking through your passport looking for the big green visa sticker that you won’t have.
Lots of things like booze, cigarettes etc on sale in no-mans land but only 120% of it is fake.