Here are some proof:

http://www.tf2outpost.com/trade/5433411 - Blizzard TC (7.8 buds) rejected, Misty Beak (7.8-9.2) rejected, 9 pure + 8 keys rejected, Scorching Milkman (7.1-8 buds) rejected, 7 buds + TS bills rejected,

http://www.tf2outpost.com/trade/8607550 - $280 (about 8.2 buds if you count $34 as 1 bud) has a buyer willing to trade in a month

http://www.tf2outpost.com/trade/7721285 - 8 buds offer rejected since he already got an offer of 9 according to seller. Had an offer of $290, which is around 8.5 buds.

http://www.tf2outpost.com/trade/8215816 - Rejected offer 7.5 pure, Had a buyer and he was very interested.

In conclusion, 7.5 is to low because everyone declined offer less than 8. Some people even offered 9 or more so it looks like 8~9.3 is a good range.