Newbie Advice: Vintage Card Grading variance (no doubt a common topic)

[oldschool73]

Hi,
After a 30year absence from the hobby, I am back...and my have things changed. I've decided to stick to Vintage Topps as there are too many mid boggling choices for new cards (one reason I left the hobby in 1990)...

Grading: What's the real skinny? I bought 6 HOFers from the 50s from a well respected dealer via multiple auctions on ebay-had them graded by SGC-and all came back .5-2 grades lower than the dealer had "raw" graded them. Fortunately, when I pointed this out-I was refunded (minus grading fees) for which I am grateful. However, what expectations should I have? My current data/experience suggest over grading to be common. Admittedly, a .5 variance seems reasonable (even though the pricing really takes a hit)...but a 1-2 grade variance?
No doubt this has been discussed ad nauseum..but , before I leave the hobby again, can the gurus on this forum please advise?
Thanks,
OS73

[leftygrove10]

You should post this question on the main page.

[oldschool73]

Thanks for advice. Will do!