I was coming into Poipet once and the line was FULL of unwashed dreadlocked backpackers. My back was really hurting bad and since the line was long and slow, I asked an agent for a chair showing him my Long Term Visa in Cambodia, he took me right to the front of the line to stamp me in. Nice guy.
Let me also note that if you saw me ordinarily, you would hand me spare change out of pity. However, I know enough about life to understand that CLEAN AND GROOMED makes life easier when dealing with authority. There is a market right next to the border where one can buy things like a clean tshirt, hair ties, etc to make yourself look presentable.