If you are grabbing embeddings from other users, there should be a link to the original model used for the embeddings. There are probably solutions for recovering the original text from the embedding and you can also just reembed the text yourself to compare the resulting vectors. But if you're grabbing enough of them that you're trying to make comparisons, you're giving some level of trust because at that level you might as well do the embeddings yourself. Additionally, if the embeddings are already being used in a recommendation system I'd imagine that they are there because they are useful and help increase the organization of the content - so I'd expect that there is less incentive to find embeddings that are maliciously  inserted by a user.