White splotches on Catnip leaves & yellowing at base

[Oak Seer]

Just received this a day ago now, as a gift, and the white splotches (which were on it when received) look almost similar to how bleach would stain your clothes! I see no mites, bugs, no webbing either, the spots aren't on every leaf! I've read many articles and forums and none seem to be exactly what I'm looking for. So sorry if this is a common question; I'm new here / new at "seriously" gardening.

Some of the leaves at the base are yellowing as well, only two small ones, seems to do with uneven watering. But the plant is otherwise healthy. I do know this was purchased from Walmart, if that matters!

Do we know what this could be? Would it be wise to exchange it out for another catnip plant or can I 'troubleshoot' and fix this?

Pictures for reference: http://imgur.com/a/3Ti0M
Thank you in advance!

[applestar]

The tiny white marks look like sucking insect damage. Look again very carefully at the underside of the leaves. Returning/exchanging won't help if their inventory is infested. Where do you live? Is it already warm there?

The yellowed leaf looks to me like it was dried out once, but not for long and not a major issue since catnip is drought tolerant.

[Oak Seer]

I see nothing under the leaves, but to be honest, it's entirely possible I'm missing something!
I did use my (mostly HD) camera on the micro setting to get a better look and it seems all clear- but I have to say it does seem like insect damage!
Perhaps Walmart had an infestation, treated it and left the damaged leaves on?

(North) Florida, and yes it's pretty warm already! 70s~80s fluctuating currently.