Haven't seen the ad, but eBay is often a good place to find holsters, grips, cleaning supplies, and even S&W parts at lower price than you can find anywhere else. Go figure . . .
I'll beat the mods to it.
Ads are driven by search engine data.
Several threads with similar statements, search forum and you will more detailed explanation.
You can help the forum and get rid of those annoying ads by making a contribution.