All the FFP cells in the world are made by five or six companies and then resold and resold through OEMs. When those primary manufacturers end up with a bad batch of cells they mark them Grade B and sell them at a discount. The reseller will often forget to include that fact. Some resellers thus have started advertising Grade A to differentiate their listings.
When I was building a 48V off grid system for a cabin
, what I found dealing with Chinese sellers directly is that they are more likely to "lie by omission" than directly lie. Say you find a listing on alibaba or similar site and it doesn't say new and it doesn't say grade A however it also doesn't say used or grade B. What are you getting? It is very likely you are buying
used and/or grade b (reject) cells that have reduced capacity. They rewrap them to look new and slap a new lower Ah sticker on them. They didn't "lie" you just assumed because here in the US used products are normally explicitly marked that way.
Another thing to check for is the specific energy (Wh/kg) and energy density (Wh/L). Grade B or used cells will be lower. In the product photos if you see the warranty qr codes are removed that is another good sign they are Grade B or used. Once again all lies by omissions.