We both agree that the simpler, the better. However there are some stadistics that would make the tooltips even better, let me show you a picture of what I think would be a better tooltip:

Item name
Subtitle
Item requirements
Item description

AuctionMaster Stadistics (Server/Side)
Auctions Seen: (X)
Vendor Price (X)         $ ($X)
H.Market Value (X)    $ ($X) / $ ($X)  <- User defined stat (Low/High/Average/etc): bid / buyout from ALL of the scans
A.Market Value (X)    $ ($X) / $ ($X)  <- User defined stat (Low/High/Average/etc): bid / buyout from ONLY the last scan
Sold (X) Bought (X) Failed (X)

There should be a tab in the configuration window just for tooltip options, letting the user turn on and off lines of information in the tooltip.

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Where:
(X) = Number of Units in your bags
$ = Unit Price
($X) = Number of Units * Unit Price
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Tooltip example:

Glyph of Dispel Magic
Major Glyph
Classes: Priest
Requires Level 18
Use: Your Dispel Magic spell also heals your target for 6% of maximum health.

AuctionMaster Stadistics (Alleria/Alliance)
Auctions Seen (50)
Vendor Price (7)        1s (7s)
H.Market Value (7)    5g (35g) / 10g (70g)
A.Market Value (7)    2.5g (17.5g) / 3 (21g)
Sold (3) Bought (5) Failed (2)

Would be nice to have it neatly formated, as in bold face and colors.
Maybe it would be a good idea to show all of the AuctionMaster info in a second tooltip that it's anchored under the ingame tooltip. (I think Auctioneer does it)