Vendor Express is only just now a couple of years old. It’s Amazon’s gateway into establishing a wholesale relationship (referred to as 1P) with sellers. Essentially it is their vendor “lite” program. The difference between Vendor Express and the regular, invite-only Vendor Central program is that with VE anyone can sign up. Anyone can also place their products up for offer to wholesale to Amazon.
When you do this, Amazon can either accept your offer or decline the price you give them. If they accept, this opens a number of vendor tools for the seller (AMS, on-page coupons, and a couple others). Historically, however, this is where sellers hit a snafu. At this point, Amazon takes “control” over the detail page listing for the product. When they do this, they tend to follow extremely outdated and inefficient style guides that, for the most part, un-optimize the listing.