I just would like to post this to give other travellers some more information about on land transportation from Bangkok to Siem Reap. and i hope this would help somehow.
(i just dont know where else can i write this ;p)
Nowadays the thai government bus company provide direct bus from Bangkok to Siem Reap,
which you can book the ticket directly at the Mochit 2 Bus Station , on the first floor, or through this following website in advance
you can also call to +66 2872 1777 or if u are already use thai sim card : 02 872 1777
you will get the payment code, and you can pay for the booking at 7-11 convenient store (provided everywhere in thailand), then keep the receipt to get the real ticket at the bus station on the departure date.
it costs 750 Baht/ ticket and the bus leaves daily from bangkok at 9:00 AM in the morning.
and from Siem Reap back to Bangkok , the bus leaves at 8:00 AM in the morning.
This option is the best way to avoid all the scam at the border, well, generally, the tourists who buy the ticket from agencies on Khao San Road have to change the bus at the border and got asked to pay more for some other stuffs. While the government bus has the priority at the immigration board, and if you have some problem with your visas, the staff of the bus will help u figure it out,
at first, you gotta get off at the office where they arrange the visa for you (except thai passengers) the bus stops here about 20 mins, and they also serve the passengers a meal box in the bus. Then, 8-10 mins after every passengers have to get off at the thai immigration office to get departure stamped, and then you have to walk to the cambodia side to get the arrival stamp, that's where the bus will wait for u.
I saw some tourists who just did the travel by themselves spending so much time to search for a bus or a transport from the border to siem reap, so i felt good that i took this bus directly from bangkok. if i could get a chance to travel to Cambodia again, i would definitely take this bus again.
Besides the BKK-SR route, they also provide to route from Bangkok to Phnom Penh, which costs 900 Baht, the bus leaves at 8 AM in the morning as i remember. and For other international routes , theres a bus provided from Bangkok to Vientiane , Laos , and Pak Se as well.