The deal over here is, you have no business selling baby formula ANYWHERE if you are not a retailer buying directly from a brand or brand authorized wholesale distributor. (AKA you have a legit business!)
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There are FB groups for selling and trading formula. You can't sell it on marketplace, but I'd try the formula groups. You can also ask in local mom groups if anybody wants to sell or trade for the kind your baby does tolerate.
Sellformula is NOT a BBB Accredited Business. To become accredited, a business must agree to BBB Standards for Trust and pass BBB's vetting process.
Real estate agents often suggest that sellers either accept the first offer or at least give it serious consideration. Real estate agents around the world generally go by the same mantra when discussing the first offer that a seller receives on their home: The first offer is always your best offer.