If the frame is not damaged and, most importantly, will fit you well, then it will be fine assuming the price is right. Frankly, the differences in frames on low and medium priced bikes between different brands are insignificant. In fact, Giant makes a lot of frames for a lot of the other big brands, so you are often just paying for the brand name, the components and the warranty when looking at a complete bike.
BTW, you should be able to get new bikes and parts for just a little above cost if you work at a shop. If you can, it's worth taking advantage of!