One huge red flag for me by the way was when I was looking at their website, they had a paypal link, but did not see any information about paying with credit cards. I did not spend much time searching around though.

I would be very cautious of anybody who did not take credit cards, as with Paypal or checks, etc, the options to get your money back are significantly less than disputing it with your credit card company.

Their terms also list a fairly long list of conditions they can raise their prices even after they have final payment including things such as

the additional transport costs demanded by the transport company for the means of transport are divided by the number of seats of the agreed means of transport

So if they can't fill up the bus, everybody on the bus has to pay more.

It may be standard language in tour agreements, but they seem to have a long list of reasons they can start collecting additional money from you once you get there.