Who you compete with
The cheapest offer is not always the seller who can take the Buy Box.
Other repricers
A typical repricer uses one action for the whole offer list. An FBM seller with slow shipping, and Amazon Retail itself, pull an FBA price down with them.
PricePulse
You set a separate move for FBA, Seller Fulfilled Prime, FBM, and Amazon Retail: Beat By, Match, Price Above, or Ignore. The gap is a flat amount or a percent. FBM can match landed price. Amazon Retail can be ignored.