So I have seen many articles claiming opportunity in the Fulfillment By Amazon or Merchant programs. I have worked for a seller of multiple selling channels, and I am outlining my experience as a piece for your research.
Common Day to Day Issues
Fraudulent Returns – It is known that Amazon and eBay accept mostly every return, I found out this is because of their policies.
What ends up happening is you have this enttity trying to create a valuable return process for the customer, and a small amount of abusers. What smart fraudsters do, is they buy a new item for which they have an old, or nonworking version of, they replace the new one with the old one, keep the new and return the old as if it is what they received. Some fraudsters just replace the item with something similar, like if I bought a small 1 oz battery, they would send back a small 1 oz rock, or similar sized item.
Amazon automatically accepts most returns and provides return materials, sometimes (if the transaction is elgible) they charge the seller for the return. Ebay gives a little more control to the seller, as the seller can accept the return or fight against it. It cn still be similar as the buyer just has to open a case, and if the fraud is not spelled out, or if it looks legit (which is easy to fake), the return is accepted and funds are refunded automatically, you can appeal though and if you can prove sufficiently that it is fraud, then you are good.
Listing Tampering – This problem manifest in different ways between Amazon and eBay. Amazon tries to make multiple sellers list under the same listing. But FBA is also very lenient towards sellers changing the listing. What often happens is another seller could have 0 inventory of item but they change the name a little bit and now any orders made will appear wrong to the buyer. So if you sell a covers for the iPhone 10, another seller changes that to a different number like 8 or 7 and it negative affects your sales. You get customers wanting the item and getting something that is not as described, or customers disregard your item as it is not the iPhone 10 covers they are looking for.
For fraudulent returns you can combat if you have some kind of serial number system in place where you have proof that you know which unit you sent to who, and can check when you receive it, best to have pictures, you could use a software or paper to write what serial number what order received.
For listing tampering, you will need to keep a constant eye on your listings, or your orders so you can catch it before it goes out, this depends though if you are doing FBM or FBA. Changing the listings could yield negative reviews, returns for wrong items received, or lost of sales; all will negatively influence your seller ratings.