How I select a folder
I first make sure it fits nicely into my hand and is confortable.
I visually inspect the knife for discolorations or problems in the fit and finish. I look srait down it lengthwise when it is both open and closed to make sure it is not warped or the blade is off-centered. I make sure the pieces line up and are firmly attatched and that all moving parts are in order, especially the lock. I also make sure there are no cracks or stains in the blade or handle materials.
I open and close the knife to test the lock. I do it very slowly and delibratly at first then I will open it at a more natural speed and then very quickly (if it is good manners, some merchants dont want you giving it a hard crack). I look for consistancy in lock up, and if it jams at any point. I hold the handle and the back-spine of the blade firmly in either hand and test to see if it has any wobble in any direction when it is opened and locked.
I look to see if the blade steel is designated on the blade and if not I will ask the clerk. Each steel has different advantages and disadvantages and I do research here to determine what steels will best siut my needs before I start shopping.
Other things I consider are the blade geometry, is it good at cutting, stabbing, chopping ect. I also check to see if I like the look of it, or if its looks are apropriate to those I will be around everyday....or if I even care about that

I consider if it has a clip (if it is strong, might tear up my pants etc.) or if I will need to get a sheath for it.
I dont worry too much about the edge sharpness in the store because I know I am gonna sharpen her up as soon as I get to my house.
I will say that there are some very good knives that can be gotten at very reasonable prices. But you can definately feel and see the difference in the higher priced brands due to the better quality control and most often better materials. Once you have spent over 100 bucks on a knife it is hard finding anything considerably cheaper that will satisfy you. I think you can find some Japanese brands in particular that make good folders that are a great value for the price.
I almost forgot...Welcome to Bladeforums!
Hope this helps a bit....I am sure I prob missed some other important aspect.