Our trip started off with our guide collecting our passports, and money for exiting Vietnam and for Cambodian visa (not necessary). The guide was asking for $25Usd for the visa fee. One traveller complained because he was asked to pay $35Usd. Us and some other travellers asked to pay the visa fee ourselves at the immigration office. We had an idea that the visa fee only cost $20US.
The guide then told us that the bus wouldn't stop at the immigration office. It would stop at a restaurant after the border. If we chose to get our own visa, we would need to hire a motobike to get to the restaurant ourselves. If we gave him our passports and money, he would take care of everything and we would enjoy having lunch. We still chose to work our own visa.
2hrs after leaving Saigon, we arrived at the border. The bus stopped at the Vietmese immigration first. We all got off the bus and we all got our exit stamps. From the Vietnamese immigration, you could easily walk to the Cambodian immigration (like most people there did). Since that our bus waited for all of us, we were asked to board it and we took a 2sec drive there instead. Again, we all had to get off the bus (including the people that have already paid the guide). We filled-up some forms and submitted our photos. 30-day visa fee only cost $20Usd regardless of nationality, and it was clearly printed on the wall. After getting our visa, we all checked-in at the immigration office. After that, the people who (over)paid the guide in advance went back to the bus and went to the restaurant. The rest of us who requested to pay our own visa fee were sent to a different exit. We were asked there for our vaccination record (not necessary). If you didn't have it, "Ok, one dolla is ok too".
When we left the building, a bunch of motobikes were already waiting for us outside. A ride to the restaurant cost us another one dolla per bike, maximum 2 people per bike. When we arrived at the restaurant, the rest of the people who went ahead of us were just starting to eat, so we ordered some food too and joined them.
Some of the roads from the border to Phnom Penh were under construction so it was a very bumpy ride for a few hours. Our bus stopped at Psar Thmei (central market). We walked about a km to Boeng Kak, then we checked in at the Grand View Guesthouse
The streets running along the Boeng Kak area is small and packed with lots of tuk tuks, motobikes, cars, and people. Guesthouses there are on top of each other. You'll be lucky (or have to pay more) to get a room with a good view of the "lake".