Siem Reap to Bangkok from land, HELP!!

I am now in Cambodia. I cannot type Chinese, but you can reply me in Chinese.

We two go to Cambodia from Bangkok by land(bangkok ~ Aranya, Poi Pet: car).

And when we first time go pass the border of

Poi Pet to Cambodia, we we were "cut" by the government cars staff, nearly 30$ per person. ( 7$ service charge, and 22.5$ for the car fee. ) But we have bought the re-entry VISA before we leave Thailand.

We are now in Siem Reap.

In about 9th, We are going to go back to BANGKOK from land by bus, then fly to Guangzhou from Bangkok. I want to ask, if there is any problems when we go pass the border again( by bus)?

What is the normal process when we go pass the border by bus ?

Will them cut us once again for any unknow service ?

I am quite worried. Please help us.