Purchasing a bike is one thing, but if you are planning to be going out into the wilds and/or risking your neck on adventurous tracks, you also need to either be competent at maintaining your bike yourself or know a bike shop that you can trust to do the right things when it comes to servicing.
You can tell how serious a shop is about good quality mountain bikes by the brands they stock. If they sell Marin, Specialized, Giant, Cannondale etc, then you know they are a proper mountain bike shop. There are some bikes - especially full suspension bikes - that you can buy from generalist retailers that look like mountain bikes, but aren't. They are much too heavy for a start. I recommend only buying a full suspension mountain bike from a recognised, quality manufacturer.
A good bike shop will give plenty of advice, will make sure you get one the right size, and will let you try it out. They will also offer a free service a few weeks after the purchase, to check the bike and adjust the tension of the cables once they have bedded in.
I have personal experience of four or five bike shops, and can recommend Edinburgh Bicycle Cooperative, near Meadow Park in central Edinburgh, and Sandy Wallace Cycles in Inverkeithing.
Retailers & Servicing
Edinburgh Bicycle Cooperative is a large shop with an extensive on-line business. They have expanded rapidly over the last few years with stores now in Aberdeen and northern England. They offer a wide range of pretty much everything you could need, and offer several levels of expert servicing. Watch out for their January sales, where you can pick up some big discounts on bikes before the new year's range comes in. The down sides are accessibility if you don't live in Edinburgh, and that the shop can be extremely busy at peak times. I don't have personal experience of the Aberdeen branch.
Sandy Wallace Cycles is a much smaller shop, but it sells top quality bikes and the staff are experts. It is much more accessible for those north of Edinburgh, being just a couple of minutes off the M90 with free parking close by. Their workshop offers an excellent level of service
MOUNTAIN BIKING in East Scotland
All photographs on this site copyright Chris Stamp, except where otherwise indicated