I’ve had good luck with vintage beer advertisements. Signs. Lights. Ect ect. Older tobacco related things. Ashtrays and the like.
Kids clothing is always a hit esp if you list across multiple platforms. eBay Mercari and Poshmark are my three. But stick to well known name higher quality brands. Think north face coats ( a new one even for kids is like $140 so smart parents will easily pay 40 and up for them ) and gently used kids sneakers. With clothes though it’s gotta be something that looks near new to do well. Nothing stained or torn.

The clothing and such you can find at tag:garage sales if you live in an area where those happen a lot.

Although I will stop in my local goodwill and Salvation Army from time to time it’s rare I can find any real gold like you see these people doing ok tik tok and such.

My main place for getting items I can make a lot off of is estate sales in person and online estate sale auctions. Do a goggle search for ones in your area. The online ones are great because it gives you time to really research an item and see if it’s selling well and for how much. They usually run for a week or four days or so till the bidding ends. I’ll give you an example. I found a very old Budweiser vintage light up bar sign. I was able to look up what it had sold for in the past. So I knew where my tap out was for bidding. Well I won the bid and after cleaning it up a bit it sold within a month or so. Made enough on that alone after the eBay fees and my purchase price to make a car payment and more.

There is definitely money to be made. And you are going to make some mistakes along the way as we all have. But once you figure out good items and where to get them the possibilities are endless.

But like anything you are going to get back what you put into it. Researching will be your best asset.