Google has been pushing the Nexus 5X and 6P with frequent sales since they came out, and it looks like there's another promo coming into effect for Valentine's Day. The Nexus 5X on eBay the yesterday was only the beginning. You can get $50 off a gold Nexus 6P or a Nexus 5X, but you might not see both discounts at all retailers. It's actually a bit of a mess.
The best place to go for all the discounts is the Google Store. There, you'll get the gold 6P deal (32GB $449 and 64GB$499), as well as $50 off both size variants of the Nexus 5X ($299 16GB and $349 32GB). You get the same options on Amazon for the gold 6P and 16GB 5X, but the 32GB 5X isn't on sale. The 6P is out of stock at the moment, though.
If you prefer to head into the real world to visit a Best Buy, the gold 6P is on sale there, but the 5X is not. On the flip side, B&H has the 5X on sale (both sizes), but not the 6P. If you want that $50 credit on the Huawei Watch, that appears to only be on the Google Store, so you'll have to get your 6P (any of them) and watch there.