Beware online sites that are too cheap or have underground or backwater or other terms in their names. May be a good idea to figure out why your panther passed away...was it old, sick?
Lol

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Underground and Backwater are great sites actually. As long as you understand what your getting when you buy from them.
The reason underground and Backwater get a bad rap, is they sell pretty much exclusively WC animals. Freshly imported alot of the time. Those animals are going to be in rough shape, they are going to have Parasites, and even if they do, (as they rarely do) have a CB animal it's been exposed to a facility that is mainly setup for WC animals, and thus will likely inherited parasites.
This is a good thing, for people that know what they are getting into. Fresh bloodlines for breeders are needed to keep the chameleon world going. Both also tend to get more exotic species, not yet having established Captive breeding, or has had little interest, or low imports.
Backwater and Underground keep this hobby running. They are the ones that bring in a large portion of our imports, without them we would have nothing but a inbred gene pool with no new blood, which would quickly come to serious issues.
For a pet owner, especially a low experience one, buying from them is not a great idea. Not because they are a bad business but because there animals are WC and that's a different league of care and requirements. WC are always cheaper, thus is most of their stock. It's cheaper because the work to acclimate, and the vet bills required are high. So first time owners, or those with little experience but from them and their animals die. This isn't their fault, it's the nature of WC, doesn't mean that we can just forgo WC from our stables. Though new keepers should.
So TLDR, nothing wrong with Backwater or Underground, the OP should Avoid WC Animals, and buy a CB animal. Which in turn will have them not dealing with Underground or Backwater.