eBay's a decent place to buy bitcoin quickly if you're not trying to go through the verification that most exchanges ask for, but some sellers also do ask for some forms of ID and you're going to pay a pretty hefty premium for the convenience and the risk the seller's taking by selling a digital product on eBay as the seller has virtually no protection from fraudulent buyers with a digital product.
Paxful and
LocalBitcoins are two other P2P trading platforms that can also be used for buying Bitcoin through various different payment methods; I personally use Paxful very often and I've had nearly no issues on the site.