The only place I see a grammar faux pas is in this sentence (emphasis mine):

> Spend less time on tracking down lost orders and focus on building great products.

It should be "Spend less time tracking down..."

The bigger issue is that nearly every sentence breaks in awkward places due to the layout of the site.

Examples:

  Safely hold payment information  
  without charging until you're ready
  to ship.  

"until you're ready to ship" is a singular concept and should be on the same line.

  Our checkout design is responsive
  so your product sells itself on any
  desktop, mobile, or tablet device.

Same: "any desktop, mobile, or tablet device" should be on the same line.

  Allow purchasing directly on your
  site with an embedded checkout
  overlay that’s elegant and secure

"an embedded checkout overlay" should be on the same line.

Similarly, none of the emphasis phrases should start halfway through a line and break:

  take pre-
  orders in person

is hard to read even though it's a key point.