Originally Posted by Russ Roth

A real shop will be your local shop or LBS. A shop that relies on bikes as their primary source of income had better be able to build a proper bike or they won't last long.

Looking at the GT, I could see buying it and dropping it off for a tune and still pocketing 200.00 if that's your budget range. Buying used as letrebici suggests can be a good way to go. Unfortunately if you don't know what you're looking at its also possible to waste a good deal of money but a bike that's been a wall hanger is often evident, if it hasn't been you need to know what to look for. My typical suggestion is that you don't get anything 7sp as its typically a freehub/freewheel design which is just outdated crap and the issue with both the trek and giant I listed above. Freewheels were fine when rear spacing was 127mm or smaller and they were produced with better materials, now that they're 135mm wide there's too much unsupported axle and they're bottom end products with bottom end materials. I also look for double wall rims as a start as they'll typically be a stronger wheel and last better. After that the sky, and your budget is the limit.

Like letrebici I also dislike coil spring forks, but upgrades are always possible. I was limited to 800.00 for my middle kid's mtb, and had to stretch to that price in order to get a frame that had real off road trail/xc geometry. A month later I could splurge on a previous generation SR Suntour Epixon air shock with remote lockout and 34mm stanchions to make the bike real off road capable. Reading reviews can matter a lot, though they don't always well cover the lower end to mid-range products. Suntour for example is often looked down upon since its typically what you find on the cheapest bikes like all of the bikes I listed above. But they also make world champion level shocks and the one I bought was equal to a rockshox judy gold, not amazing or top end but decent enough for a kid. You just have to watch how much you intend to upgrade or you might have been better off saving for the nicer bike to begin with.