Dishonest customers are huge problems for many companies, and shoplifting costs U.S. retailers something like $50 billion a year. Of course, you have to view that in the context of total retail sales, which are on the order of $4 trillion a year. (Employee theft, by the way, costs retailers about the same amount as shoplifting, so it's not just the customers who rip off companies.)
Controlling customer theft and dishonesty seems to drive a lot of customer-hostile service policies, and I've occasionally observed a "they're all trying to rip us off" attitude among some retail employees and call center agents.
"If some people didn't abuse it, we could have a more liberal return policy," is a common refrain (substitute "repair policy," "warranty," or "customer service" for "return policy" as needed).
Using bad behavior to justify bad behavior tends to lead to a downward spiral: I've heard consumers use "they screwed me because they wouldn't take back my broken laptop" or "they extended my contract without telling me" to justify their abuse of company policies.
Some companies--for example, Apple--seem to have taken the approach of higher service levels even if it risks some customer abuse. Apple is famous for being willing to fix computers out of warranty and accept returns even when the customer probably abused the product. Costco has a similarly liberal return policy, and both companies enjoy a reputation as an easy place to do business--and they probably charge slightly higher prices to support the customer abuse.
Other companies, like Best Buy and Wal-Mart, seem to be willing to sacrifice the customer experience for some incremental improvement in loss prevention. Purchase anything in a big box from Best Buy and you're likely to get hassled on the way out by a security guard, even if you're the only customer in the entire store and the guard watched you pay for it.
There's no way to eliminate dishonest or abusive customers: it comes with the territory of doing business with the general public. The key is to recognize that only a tiny fraction of customers are thieves, and strike a balance between limiting loss and annoying the vast majority of honest customers.