Google has warned over misuse of Event markup
[webmasters.googleblog.com] whereby coupons or vouchers are showing up in search, instead of the events. This also applies to any non-event items being annotated with the event markup.
It says it'll take manual action and report it in the Search Console, and may result in structured data for the whole site in question not being used in SERPs.
Here's and example
Event markup information [developers.google.com