When is it too good to be true?

[SnowflakeMama]

Hello All,

After another post in here I had just decided to wait a while before getting a new zoom lens, but now I've come across an opportunity to purchase a used 24-105mm f/4 L IS USM for $600. I don't need this lens right now, but it won't break the bank at this price and if this truly is a good deal I'd like to consider it. According to the seller the lens has one very minor scratch that does not affect photo quality and it is priced with that in mind. I tried to Google how much it would be to replace the glass if I find that the scratch is noticeable, but obviously my search terms were not right because I just kept coming up with reviews for the lens itself.

So I am wondering...
How do I know if this is too good to be true? Is it crazy expensive to replace the lens if the scratch is noticeable in photos?
In addition to actually trying the lens out, what else do I look for (or ask) before agreeing to purchase?

And also... the lens I had originally been considering was the 24-70mm f/2.8, and when I compared the two online the only difference I found that I didn't really like was that the 24-105 is only an f/4. But I was also planning on picking up a 50mm f1.4 or f1.8, which would give me the larger aperture for when I find myself in low light situations. It seems to me that with the 24-105 and the 50mm I'd be covering all bases. And if it helps, I photograph my kids a lot (far more than I probably should, lol), along with some travel photography, landscapes, etc., and I almost never use a flash (I don't even own one except for the built-in). Really the only thing I can't ever see myself photographing is sports.

And if you don't already know... I think I might be the newest newbie out there, so feel free to speak slowly.

[brianxlt]

The price is good if the scratches truly are not an issue with image quality. If you can attach it and shoot a few shots to see for your self that would make or brake it. if you can't see if they can take some closeups of the lens/sratches so you would at least see them for your self.
As for the 24-70 F2.8 or the 24-105 F4 / the F2.8 does make a difference, but if you are not worried to much about low light the 24-105 with IS for a general walk around and shot the kids or what not is great for that and the more reach you get. I have the 24-70 F2.8 and the 50mm F1.4 and love them both, but don't always need or use the F2.8 more like F4 or F5.6.