FLAT black?? A gallon?
That's enough paint for eight carts
I'm not a painter, but I stayed at the Holiday Inn Express....
If your cart has no scratches, sand it with 600 grit and spray it. Check with a paint store for an additive (flex agent) so the paint won't chip. They also have adhesives that helps paint stick to plastic.
Flat black will show few blemishes and with a gallon you could touch it up all you need! You don't even need to make it flow for a gloss.
Seriously, wait for a real reply. This cart was sprayed with rattle cans. No clear coat, no wax, nothing. Scuff and squirt. Good Luck!