I placed here some snipes on a Seller (gandalf_1952) I transacted before. And I have no existing cases.

After the bids on (110810350442) and (40027067640 ended, myibidder remarked 2 Status I hadn't encountered before.
1st style: My Status: Your PayPal account is not linked to your eBay account
2nd style: My Status: Seller's requirements not met

After these bids, I was still able to snipe on other sellers and won.
Thanks

The restriction is set per listing, not per seller. That means if you could bid on other listings, it does not mean you can bid on all listings from the same seller.
When not sure, please place a minimum manual bid first. If your manual bid goes through, the snipe should be fine as well.

Also, if you have PayPal account, then you have to link it to your eBay account to avoid blocks due to the reason #1:
http://www.myibidder.com/forums/viewtopic/647/your-paypal-account-is-not-linked-to-your-ebay-account/