Execs at public companies always have to schedule their stock sales many months in advance. They cannot sell on a whim. The SEC is very strict about this and they do punish transgressions. Most execs sell stock on a regular monthly or quarterly schedule. Since execs are commonly paid primarily in stock, of course they will always be selling stock. It's just financially prudent to diversify your holdings no matter how much you believe in the company. As a result, you will almost always find, if you look, that execs in any public company have recently sold stock. It may even appear that they have sold a large percentage of their overall holdings, but this is often just because either they sell as they vest (again, generally considered wise financial practice) or because their stock is mostly in a different share class which needs to be converted before sale (and the "percentage" is actually a percent of their holding of the converted share class).

So I'd be extremely skeptical of any stories accusing executives of dumping stock, they are almost always benign.