Amazon FBM Business is Amazon Fulfillment by Merchant.
Fulfillment By Merchant (FBM) is when the seller is in control of his entire handling and shipping process.
Instead of paying a service fee and shipping inventory to Amazon to handle, the seller uses his or her own resources and sends the items directly to the buyer.
As a Pro FBM Amazon seller, the subscription fee is $39.99 per month.
FBA (Fullfilled by Amazon) is Amazon's warehousing and fulfillment service that allows sellers to send inventory to an Amazon warehouse and have their orders shipped by Amazon.
FBM (Fulfilled by Merchant) is a fulfillment method in which the seller takes full responsibility for storing inventory and shipping orders.
Amazon deducts a referral fee each time a product unit is sold.
The referral fee is a percentage of the total sales price and is usually 15% in most product categories; however, it differs in a few categories, going as low as 6% and high as 45% for Amazon Device Accessories.
You can manually change a listing's fulfillment type by simply opening a listing page and clicking on the "Offer" tab.
Under "Listing Details" you will find the "Fulfilled By" field.
Click on the dropdown to select either FBA or FBM. Now simply click "Save & Publish" and you're all done!