Just because you call it a replica doesn't mean you are out of the woods. Most replicas are nothing more than items that infringe the trademarks, trade dress, and copyrights of other companies. The sellers who hawk replicas are banking on the fact that their items are so close to the real thing that you or your friends won't notice the difference: if that's the case, more often than not they've crossed the line into trademark or copyright infringement, and depending on the facts, could be facing civil or criminal penalties, or both. My advice: if you want quality, buy the real thing.
It's illegal to sell counterfeit goods, and to try to fool consumers about the source of products. When products copy the original including a copy of its trademark, they're trying to "pass off" their fake, counterfeit, illegal product as if it was the trademark owner's, in violation of the owner's trademark.
A replica/clone that doesn't infringe on a trademark by falsely designating its origin would be legal, but the replicas and "inspired by" products you're probably referring to invariably at least violate a trademark owner's "trade dress" (the look, shape, feel, packaging, colors, silhouette, etc. of a product), if not also the trademark itself.
Replica sellers are basically trying to help the cheap consumer pass off the product as a real one, so they're not going out of their way to make products with enough differences that consumers would see right away that they're fake - like an upside down Nike swoosh. On the contrary, they're doing their best to make a convincing fake. They want to convince you the buyer so you can convince anyone who sees you with this product. Bags and watches are all pretty much the same in terms of function, and there's not a huge difference in quality, so what makes some original designer ones so high priced is precisely what the replicas are trading illegally on -- the trademarks. The Louis Vuitton patterns. The prestige watch brand names. Replica sellers make an explicit disclaimer that their products aren't original and aren't exact copies so they don't violate any copyright. And they don't, because bags and watches aren't copyrighted, they're trademarked, and the replicas trying to "pass off" as the originals are violating trademark rights, even if they say theirs are better values when compared to the originals. That might be true, and might be an argument why trademark law should be changed, but until it does, replicas infringe.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.