Reputation is everything. I have been buying (and selling) magic cards on eBay for years now. I bought all my power-9 via eBay, and all of it is real; some of the sellers were card stores, some were individuals with positive feedback (sometimes relatively low feedback, but still positive). Yes, people have attempted to sell me fake cards before, and the fakes range from laughably bad to really really good. The fakes being printed in Asia these days are quite good and can fool a novice, but they still aren't perfect (especially the "feel").
No matter where/how you decide to purchase power, the absolute FIRST thing you do is spend $5-10 on a good jeweler's loop, buy a few A/B/U commons—in particular, buy 3-4 different IDENTICAL alpha/beta artifacts and blue cards, so you can see what kind of color/resolution variation is natural and real, vs fake. Really take a close look at them so you get used to what makes a magic card a magic card. The rosette print pattern, the subtleties of the double-black border, the "TM" on the back of the card, font spacing, color variation, etc.… these are all subtle things that fakes often don't get quite correct. You need to be armed with this knowledge whether you're buying from eBay, social media or your LGS.
I've now gone through the dispute process for receiving a fraudulent card from an ebay seller over a dozen times, including for auctions over $1k, and won every time. Here are some tips to protect yourself. Most of it is preventative (an ounce of prevention is worth a pound of cure):
Tip #1—Pick a Reputable Seller.
Trust your gut; if someone is selling a mint beta lotus on eBay for $2k, the pictures are fuzzy and have different backgrounds, the person just joined eBay and has a zero feedback rating (or, more sneakily, has a feedback rating of 5-10 but when you read the history that feedback is all for BUYING not SELLING), you should be very, very skeptical. If someone is selling a beat up beta lotus for $4.5k, has 8 close-up pics and a feedback history of 100% (which, upon review, is positive feedback from dozens or hundreds of other people who've happily bought magic cards from this seller in the past), then you are much safer. There are plenty of great MTG sellers on eBay with long histories (DanBock and Kid Icarus pop to mind first).
Tip #2—Become Reputable Yourself.
Become familiar with eBay and use it to make a bunch of small purchases first. If you can use it to sell a few things yourself too, even better. The vast majority of disputes on eBay are "he said/she said" disputes, and feedback history matters a TON. Now that I have a 100% positive feedback of over 400, when I dispute against a seller with a feedback rating of 0 eBay gives me the win without even batting an eye.
Tip #3—Buy in the US.
If you have any doubts/reservations at all, do NOT buy if the seller's location is listed as being anything other than the US (I assume you're in the US). If the seller is from another country (even Canada), the dispute process is much more rigorous, you'll have to get sworn affidavits from LGSs or other "experts" in MTG to "prove" the card is fake. It's possible to win but a big PITA.
Tip #4—Take Pictures.
Always video-tape yourself opening the package, so you can prove what you received and what condition it was in. If it's a card worth a lot of money, open it live, on video, at your LGS, in front of witnesses. This is important to preclude the seller from accusing you of swapping out the "real" card they sent you for a fake one, which I promise they will try and do. If the seller ends up accepting your return (or eBay forces them to), video tape yourself putting the fake card back in the envelope, sealing it up, and dropping it at the post office. These measures aren't foolproof, but the more evidence you have, the more likely it is you'll win in the "he said/she said" fight.
Tip #5—Follow the eBay protocols.
eBay has a whole system for this. Make your claim in a detailed and timely manner, and be polite but firm, and you should be fine. Recognize eBay customer service can see ALL of your messages, so be polite, and be consistent, with what you say to the seller and/or eBay. First you say you want to return the item, and why, you attach pictures, etc. eBay gives the seller a window of time to respond. If they don't respond, or refuse to agree, you then escalate the claim. You'll hear nothing until eBay either decides in your favor, or asks you for more info/evidence. If the value is over $750 (I think), then a whole separate department within eBay handles it (that's a good thing—that department has "real" people looking closely at the situation, not just a customer service "drone").
In general, eBay is very buyer-friendly when it comes to this. I've never lost an eBay dispute, but if I did I would still have the backup protection of PayPal itself and my credit card company.
Buying through social media is fine, again, just so long as you're buying from reputable sellers. Most people on social media just go on "trust" and don't even pay the extra fee via PayPal to have some buyer protection. I bought a Tabernacle at Pendrell Vale from some guy on twitter I didn't know, unprotected, and everything went perfectly. Why? Because the guy is an established member of the vintage community and I knew he'd sold cards to dozens of people in the past. Reputation matters.