Hi Lina,
I would treat all mattress reviews (positive or negative) with caution because regardless of whether they are “truthful” or not they won’t provide you with meaningful information about whether a specific mattress is suitable for you or about the quality of the materials in a mattress or the mattress itself. You can read more about using reviews vs more legitimate and meaningful types of mattress research in post #13 here.
There is also more about the most important parts of the “value” of a mattress purchase in post #13 here that can help you make more meaningful comparisons between mattresses without having to rely on mattress reviews.
Selling a mattress that has used materials inside it as a new mattress is against the law in most states and isn’t a practice that most legitimate manufacturers (including SleepEZ or Savvy Rest or Sleeplikeabear) would engage in or risk doing. These are the types of mattresses that you will usually find at liquidation outlets (see post #8 here and post #2 here and post #2 here).
It’s not something that I would be concerned about if you are following the guidelines in the mattress shopping tutorial and you are dealing with a reliable and knowledgeable retailer or manufacturer.
Phoenix