… You find them all on a dating website.
Lying, though, is normal human behavior. We all use to lie if we can expect to get away with it. Moreover, lying is widely accepted in advertising. For instance, these airlines (http://www.emirates.com/english/index.aspx, http://www.malaysiaairlines.com/my/en.html) advertise with picture of pretty looking flight attendances, but nobody would expect to be on a plane with just these women. Even worse, if you take a flight with these airlines you will certainly meet the uglier variety. By the same token, it can be expected that advertisements on a dating website are heavily embellished.
By contrast, cheating is breaking a contract. It is possible only if a contract was negotiated. Some agencies that host dating websites demand a contract and they provide some kind of control, but as a rule this is an additional service that has to be paid for.
Finally criminals, one has to be aware of on dating websites, too. How blackmail originated by a dating advertisement can work is vividly described by Grisham (http://en.wikipedia.org/wiki/The_Brethren_%28novel%29). Not only blackmail but all sorts of crime can originate from a dating website. I wont dwell on that as “desynchronizing”- website focuses on communication problems. Among those criminal behavior is a marginal problem only, but a word of warning should be allowed here.