All Scotland's major towns and cities are served by long-distance bus services, known across Britain as coaches, the majority of which are run by the national operator, Citylink.
There are various discount cards on offer for those with children, those under 26 or over 50 and full-time students: contact Scottish Citylink for more on these.
Coaches are generally cheaper than the equivalent train journey and, as a result, are very popular.
For busy routes and travel at weekends and peak season suggest to your clients that it's best to buy tickets in advance from the website or any bus station in the U.K., as this will guarantee them a seat.
Local bus services are run by a bewildering array of companies, many of which change routes and timetables frequently. As a general rule, the further away from urban areas it gets, the less frequent and more expensive bus services become. Some rural areas, particularly in the Highlands and Islands, are only served by the postbus network.
If your clients are travelling a lot in England and Wales too, they might be better off with a National Express Brit Xplorer Pass, which gives them unlimited travel throughout Britain on National Express coaches.