OEM wont' be necessary good for 2 reasons:
1:/ you will never know if it's a guenine or fake
2/ you will find (many) "brand news" EOM battery that will have many cycle on it (800 is common).
You should not focus necessary on OEM but good quality. And the best way to know that, is to count on the reputation. Look for the review, not of the seller, but of the battery itself. It's not 100% safe of course, but much better than anything else.
And of course, don't trust the review posted on the manufacturer or seller website. Common sense.
Look for them on independent review website (trustpilot seems to make some money by not publishing bad comment, but their should be honest website around)
Inn my opinion it's better to get a battery marked as "replacement" (at least you know) than a so called OEM at a same review level. Because the guy who produce the fake OEM won't attach his name/reputation on the item (obvioulsy). But the "replacement" battery brand will be shown, and the manufacturer/seller count on its reputation to make money.
Reputation is everything in business (it's a basic principle of evolution by the way)
**and post an (external) review each time you buy a bad (BUT ALSO A GOOD) item,**