Everything looks brand new.
in The Commons
Is there a simple way to make shoes look like they're not brand new out of the box?
Or are there shoes available that have some scuffs or a bit of wear and tear?

Comments
All depends on the textures the Vendor provides, though it is easy enough to create the look you are talking about. You could make textures of the kind you want, can also use geoshell to add onto the texture any scuffs or dirt.
You could use this:
https://www.daz3d.com/a-touch-of-dirt-for-iray
If it is for a one off, i would simply either find a "dirt" pattern, apply it as a L.I.E. layer, turn down the gloss, and render or you could buy a dirt package like PTF Grungy Threads or DG Iray Surface Builder or a Touch of Dirt if you will be donig this all the time....
Time to come to terms with photoshop or GIMP it seems
It might be easier to just make an alternative texture for the shoe. Since you are new to geoshells and LIE, I think that would be the best way. You can find dirt splatters or whatever you are looking for any number of places and use an editor like photoshop or GIMP to mix some of that in to the shoe texture. Just make this a new texture, don't overwrite the one you have. Plus I think this would be easier for Daz as well, doing this would use a little bit less memory which could be a consideration if your PC is not too great.
There is still yet another option, too: decals. Daz Studio has a feature for using decals. The benefit to a decal is that it can be moved around easier than LIE, and a decal can cross over UV maps. And like all things Daz, there is a product that makes using them a bit easier. Rather than link the product, I will link its thread, because the thread describes what it can do and how to use it so you can determine if it is something you might want. https://www.daz3d.com/forums/discussion/151576/iray-decal-kit-make-your-own-decals-tutorial-commercial/p1
It all depends on how often you want to do this and how often you use an image editor but there are a lot of solutions...