- Obviously, if you copy too closely, you are violating copyright, which not only rude and illegal, it will also get you kicked off the site.
- Even if you change enough so you are possibly not violating the original author's copyright, you are creating a lot of bad will. We collaborate a lot on TpT. Other sellers can really help you out, especially the ones who are successful. Many of them have huge followings and enjoy helping out newbies. Don't make them angry at you.
- Copying not only shows a lack of respect for the other seller, it also shows a lack of respect for your own abilities...if you are selling on TpT, you should be able to come up with your own ideas.
Of course, the line between copying and simply using a similar idea is a tricky one and it is up to you to use your best judgement. Many formats, games, puzzles etc. have been around for years and no one really "owns" them. If you are working with one of these older formats, the trick is to put your own spin on it.
Finding your own style and niche is super important and in fact is the way to be successful on TpT. If you look at all of the top sellers, you will see that is exactly what they did. So find yours!