What some sleazy customers do is enter a higher projected tip when placing the order, which induces drivers to accept their order, but then change it after delivery to zero tip. This is a common practices among certain ethnicities....
This is a big deal with food deliveries because the tip is often up to 50% of the order, sometimes more. That commonly happens when people order a small amount of food. So essentially, they're deliberately lying to drivers to get them to pick up an order that otherwise isn't worth their time.
Obviously, that's a different issue if the driver screws something up. But customers who always bait and switch on tips should have that exposed.
If it isn’t real then they should end letting people post fake tips, paying in advance isn’t a tip anyway, it is telling someone what you will pay them to deliver your package to you, like the USPS or Fed-Ex.