Suggestion 17. Squad 1.

Marketplace sales

https://marketplace.tf/items/tf2/30025;5;u32

September 29 - $12.99 / $1.84 = 7.06 keys (7 Keys)

October 2 - $13.4 / $1.87 = 7.17 keys (7 Keys)

October 7 - $13.4 / $1.89 = 7.09 keys (7 Keys)

December 19 - $13.99 / $2.02 = 6.93 keys (7 Keys)

December 24 - $14.99 / $2.09 = 7.17 keys (7 Keys)

Classifieds

https://gyazo.com/f2267292207770eecd1911e9efa2c0ad

Summary

Sales at 7, 7, 7, 7, and 7.

Conclusion

Going with 7 here, if it wasn't obvious already :P