I'm obscuring the vendor tag to protect the innocent, since I'm looking to make a general point, not single anyone out. Check this out:
Even though I'm not showing you the tag, let me assure you that it's marked at waaaaay more than a dollar.
It's one thing to sell Dollar Tree stuff in your booth, and there's nothing wrong with that. If people want to buy it, they will. Kosh knows, there's plenty of it out there at yard sales and thrifts.
It's another thing to sell Dollar Tree stuff for more than the dollar it cost when new. Again, there's nothing inherently wrong about it, depending on the item. If people want to buy it, they will. I even do it myself sometimes (but never for more than $1.99).
It's even another thing to sell Dollar Tree stuff for several times more than the dollar it originally cost. There's still nothing wrong with it, or at least trying it. Dollar Tree and the like do get some decent stuff, after all. If someone wants to buy it at that price, they will. Never hurts to try. You never know what's going to happen.
However, if you are going to try that, you need to be sure to remove the Dollar Tree tag! Seriously. Customers do notice such things.
I try not to buy a lot of Dollar Tree merch at yard sales and such, unless it's a really awesome piece. (And there are some of those. The one I am holding in the pic is way cool. You'll have to take my word for that.) The quality is just not there, and the stuff breaks and chips way too easily for my tastes. Plus, a lot of it is really cheesy/tacky and just not what I want to sell. I like to try and have things that are different from what other sellers are carrying.
If you feel the same was I do about this stuff, one thing to know is what distribution companies to look for. You can see in the tag above that it comes from Dollar Tree Distributing. That "K's Collection" tag is a giveaway too, since that's a brand that is only sold in stores like Dollar Tree. Other names to look for are Dolgencorp (distribution for Dollar General Stores) and Greenbrier Distributing.
You've got to make your own decisions about what to sell and how to sell it, based on what works for you and your location/venue, for sure. But if you do try to make serious buck off of something that someone, somewhere originally purchased for a dollar, at least remove all the evidences of its past. You'll have better luck selling it if you do.