Order from a reputable vendor (and there are certainly some Chinese vendors that are reputable, including Fasttech (clones are marked as styled, vs authentic) 3Fvape and some others. In the US, well you can certainly check out ECF "approved" vendors, you can count on authentic to be authentic and vice versa (unless there are no clones being carried by that vape shop).
Most people run into difficulties using sites like ebay and etc. I'm not going to say there aren't any "bad" vendors, there most certainly are. But, if you check out the vendor list in ECF, they usually have a staff member (or owner) who can respond to any concerns, etc.
If you want to buy in person, I'd say check reviews and google any "real world" vendors before going there, etc.
Sometimes, clones aren't a "bad" thing exactly (well, I'm sure the creators of said vape items feel that they may be) but certain vape gear can be excellent and also pricy, and there are "known" clone makers, some more trusted than others. There are occasional times a "clone" may even be considered "as good or better" than the original, although not always. However, with some atomizers for example which may be highly desired, located overseas, it can sometimes come in useful to have access to a clone, or to try one before buying the original to get a sense of if you might like it or not and etc., etc. So, sometimes it's not so bad to get a clone
with the knowledge you are doing so.
However, for entry level vape gear and your purposes, probably getting a clone (especially if sold as an authentic) would be a bad thing. Fortunately, you will have many choices of reputable vendors right here at ECF.
Do you know what you are searching for?
Also, I don't tend to trust vendors (any of them) for removable batteries if that is what you want, I'd advise buying from merchants listed in Mooch's table of battery tests, the last cell will show a list of authentic, reputable battery sellers.
I don't know if you need all this information now, but I will link it, in case you are wanting a removable battery mod. Many people starting vaping don't start out with a removable battery, but since I'm unsure what type of vape you want, I will list the two blogs to follow regarding battery safety. If a removable battery mod is not in your immediate future, you certainly don't have to read through them, but they may be useful for in the future, and etc.
https://www.e-cigarette-forum.com/blogs/mooch.256958/
https://www.e-cigarette-forum.com/blog-entry/baditudes-blogs.7609/
Best of luck,
Anna