Here in the United States, “fair market value” on any item is determined by what a buyer is willing to pay a seller for the item. Simply put, if I have a stick of gum, and I offer it to you for ten cents, and you want to purchase it for ten cents, then the fair market value of the stick of gum is ten cents.
While real estate also has a fair market value, it is a bit harder to determine because of all the factors which go into the valuation. A property, unlike the simple stick of gum in the above example, has multiple aspects for a seller and buyer to put different valuations on. Introduce a lender into the picture, and then you have a third option on valuation to deal with as well.
Determining commercial property market value is different than determining market value for a residential property. In a residential valuation you can simply look at other recent comparable sales in the area, of similar homes and lot sizes, and determine about what a property is worth at any given time. The issue you will find with commercial property is that they tend to be one-of-a-kind properties, and you may not be able to find many local comparable sales in recent times.