I checked around myself, seems like this is a hard sell item. Most people are asking to buy for 8 keys, but with how low the demand is I could see this dipping even more. Upboat.

Very interesting... Playing devil's advocate, I went through all 14 pages on Outpost to see whether or not other people were having as much success as you. Ignoring all highballers and Sandviches sold as part of a set, this is about as much as I could find that could be used as counter-evidence:

http://www.tf2outpost.com/trade/8742307 - offer of a Black Bills for the S.F. Sandvich + 1 key (22 hours ago)

http://www.tf2outpost.com/trade/7269866 - offer of a Strange Sapper (~8.5-9 keys) (1 hour ago)

http://www.tf2outpost.com/trade/8761153 - same offer as above, by same potential buyer

http://www.tf2outpost.com/trade/8778588 - seller wants to 1:1 with a Gen. Maul (~8-9 keys), one interested (21 hours ago)

From looking at the trades currently listed, aside from yours, I can only find extremely new trades wanting to sell at 9 keys (and those obviously wouldn't have been able to find buyers yet). Let's keep an eye out for these trades selling at 9 keys and see how well they pan out:

http://www.tf2outpost.com/trade/8777240 - 1 day old

http://www.tf2outpost.com/trade/8742307 - 2 days old (see: potential counterproof)

http://www.tf2outpost.com/trade/8780329 - 21 hours old

http://www.tf2outpost.com/trade/8732842 - 3 days old

http://www.tf2outpost.com/trade/8788773 - 8 hours old

http://www.tf2outpost.com/trade/8728733 - 3 days old

http://www.tf2outpost.com/trade/8789366 - 8 hours old

http://www.tf2outpost.com/trade/8788579 - 8 hours old

http://www.tf2outpost.com/trade/8782761 - 18 hours old

http://www.tf2outpost.com/trade/8778768 - 23 hours old

http://www.tf2outpost.com/trade/8706845 - 4 days old

http://www.tf2outpost.com/trade/8383421 - 2 weeks old (unlikely...)

http://www.tf2outpost.com/trade/8468274 - 2 weeks old (unlikely...)

If a lot of these sellers end up being successful, then clearly this suggestion of 8 keys flat will be incorrect. If not, then I think it's safe to say that your success was the result of other external factors, as opposed to community-wide demand for the item.