[swarmee]

The Purple Label guy here on this board said he believes he can identify alterations and will give a Silver sticker to an already slabbed card that he can confirm is "unaltered". Superdan from blowout has an email listed on his posts where you can message him directly. As said, you need to be an expert on each type of card, their factory edges, their look, their feel, etc. Maybe you just can't trust yourself to purchase items online until you get more experience.

Having the cards in hand raw you can feel, smell, and compare them to commons from the same set. Some of the people who say "trimmed" or "fake" on a post know what they're talking about and have the experience. Many are just trained to be distrustful, and will post "fake" no matter what to try and look smarter. For most Topps sets, you can get commons from COMC for under $1-2 each. For Goudey, you can probably buy some for $5-10 each.

One thing I've recommended in the past is to look up old threads (like 1933 Goudey Set Collectors or 1952 Topps set collectors) and see who the most knowledgeable guys on that set are. Then direct message those members and send them the link and get their thoughts directly. If you make a post, they might not respond, but if you send them a direct question, they usually will.

Fakers/trimmers have gotten really good over the past couple of years, and can now fake "factory rough cuts", "factory perforations", fill in pinholes, recolor ink, remove stains, etc. Many things you won't be able to tell from online scans unless the seller is willing to take additional pictures for you, or you could match them to previous scans of the same card. Good luck to you on trying to learn this stuff.