How to shill for my eCommerce store without seeming too spammy?

Im launching my store soon, but i don't have any advertising budget, so i figured manually targeting forums and facebook groups would do. But afaik it's not as simple as "Hey guys check out my *insert thing* tnx" plus i figure admins are usually vary allergic to that sort of thing.

So im wondering what are some of common methods to get people to buy your thing or visit your site without getting banned for spamming or just being too obvious?
Im new to this so plese go easy on me D:

Don't say it's yours. Say you're selling The Walking Dead gear, go into a TWD fan page and be like "yeah, rick is my favorite too, I just bought this shirt" *insert shared post from your page featuring him.

Obviously, it's just an example, but something along those lines. Targeting pages with good engagement is key.