said 7 months ago:
@albertmora & @milan-steskal It is against Facebook’s Promotional Guidelines to use Facebook’s functions (Like, Share, Comment), but NOT using an app’s functions.
As long as you use an app and the functions within that, you are okay (assuming they don’t violate any guidelines or terms). So, just for the record, my example above is valid and within the guidelines.
As for making a competition as shareable as possible, it is not always obvious to everyone. I have seen many competitions without share buttons integrated into them.