[the 'stache]

Where is this being offered?

You can do your due diligence before committing yourself-that includes examining the seller's history (have they ever had negative marks? How long have they been selling? Have they dealt with vintage cards in the past?) Get additional scans/photos if you need. But, keep in mind some cards you won't be able to really gauge authenticity until you have it in hand. There are some good reprints out there, and unfortunately, not all of them will show clear indication of reproduction. Plus, somebody could always copy an image from elsewhere on the net. I usually ask them to take a picture of the card with their user name in the picture. Compare the pictures of the card you're considering with others you find on the net. While I won't usually buy vintage or pre-war from Beckett, I know that if I find a BVG-slabbed card pictured, it's likely the real thing. Look for any flashing red lights that might disqualify the card-color differences, printing or typography issues. If you feel reasonably sure it's authentic, go for it, but make sure you have recourse. In other words, don't buy something unless you are absolutely certain that you have protection.

Buy the card through Paypal, or a Credit card with zero fraud liability.

Once you get the card in hand, look it over with a loupe, comparing it to a similar card (ie, the same year and design). You didn't specify if its a Fleer or Topps card, but get a common from the same set, and look at both side by side. if the card is slabbed (graded), examine the slab for imperfections/signs of tampering. Examine the flip (the card with the printed information). Make sure there is only one flip. Compare the type to examples found online.

If you can share pictures of the card you're looking at, we can help. But always...always be on the defensive as a buyer.