Greyhound Bus tickets

I booked a Greyhound bus ticket on line. There was no option to choose the seat number. When I received the ticket I had been allocated the first row next to the toilets, and I was embarking on a 21 hour journey. I phoned Greyhound to ask to change my seat number and they would only do this if I paid 50% more on the ticket. This is clearly not feasible. The operator said that if you book your ticket on the phone you can choose your seat, but not if you book on line. This is useful information for other passengers- but this information is not stated on their site. I fear I am going to have a long and smelly journey!