I have a friend who's turned flipping DVDs on eBay into a fulltime job and honestly, it's a pretty unhealthy looking life. You're assessing the value of so much junk, buying it alongside weirdos all day at thrift stores. It makes you jaded from your original passion. You become like a vulture or a rat.
It's a lot of gambling on items to resell and that fries your brain over time. I remember people calling shopping and bidding on eBay addictive back in the day, and same's true these days for selling stuff online. My friend's missing valuable life experiences with this flipping shit.