7700k for $309, free shipping (eBay via Monoprice)

I picked one of these up the last time they had this offer. I'm happy so far. Clocked easily to 5GHz. Just putting it through its paces this weekend.
Got one coming from eBay, paid $299.99 for mine. Much cheaper than Newegg.
Is this a retail box cpu or a loose chip? It's tempting but I feel like there must be a catch I'm missing.
I know it's Monoprice so people are not too worried but I always feel like there is some catch when the price is kind of low on in demand commodity items like this but mine came in a sealed retail package and works perfectly.
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