My LCS has a sale every holiday, but never 75%!
I think LCS's should really push on Christmas sales, it's the one time of the year when you have non-comic fans coming into the stores looking for gifts, making the extra effort to make the store friendly would probably be a good idea.
My LCS has 2 big sales a year, one during Christmas it is usually along the following:
Silver Age comics 40% off
All other back issues 50% off
Trades not already marked down 40% off
Supplies 30% off
Statues, T-shirts, etc. 30% off
I might be a bit off on a few but it is close to that.
What makes it really sweet is if there is a trade that you want that he doesn't have. He will order it and give you the discounted price on it. Also, for good customers he will give you the sale price up to a week in advance.
My LCS, JPM Comics in Glendora California, has a Black Friday Weekend Sale.
They have a special sale from 10 PM to Midnight Thanksgiving Night. The special sale is 50% off everything (not just comics) in the store except Silver and Golden Age comics.
Friday, Saturday, and Sunday November 28, 29, 30:
Back-issue comics priced at $1 are on sale for:
15 comics for $10
25 comics for $15
50 comics for $25
Back-issue comics priced at 25 cents are on sale for:
25 comics for $5
50 comics for $9
100 comics for $15
This thread reminds me of a dealer I saw at a comic con years ago.
All of his comics (and admittedly he had a fair amount of good Silver and Bronze stuff) were marked "50% off."
Unfortunately for potential purchasers like me, his starting prices were already quite expensive, and in fact one of the other dealers told me he basically doubled his prices before the con!
Needless to say, I didn't appreciate his con artistry.
Mind you, Mile High get up to the same sort of tricks!