Sell Orders start at 6 keys. Ignoring the sell orders for 5.6 keys, due to there being no sale ranges that fit between 5.5 - 5.6 keys, as well as the fact that they're more than likely quicksell listings, along with the fact that sales in the last 30 days have been too high or low for that current range, so branching out is the only option.
Suggestion version 2.0 w/ fixed price ranges.
https://backpack.tf/classifieds?item=Starduster&quality=11&tradable=1&craftable=1&australium=-1&killstreak_tier=0
Buy Orders start at 5.48, ~5.5 keys.
Sell Orders start at 6 keys. Ignoring the sell orders for 5.6 keys, due to there being no sale ranges that fit between 5.5 - 5.6 keys, as well as the fact that they're more than likely quicksell listings, along with the fact that sales in the last 30 days have been too high or low for that current range, so branching out is the only option.
Bot.tf Sale:
https://ibb.co/1b94r5G
1 Sold for over 7 keys.
Marketplace.tf Sales:
https://ibb.co/gmVmjTx
1 Sold for $8.00/ 1.85 = 4.32, ~4.3 keys.
1 Sold for $13.86/ 1.8 = 7.7 keys.
1 Sold for $13.86/ 1.81 = 7.65 keys.
1 Sold for $15.00/ 1.82 = 8.24, ~8.25 keys.
1 Sold for $19.99/ 1.87 = 10.68, ~10.7 keys.
SCM Sales:
https://ibb.co/PGBrzg8
1 Sold for $13.38/ 2.35 = 5.69 (nice), ~5.7 keys.
1 Sold for $14.97/ 2.35 = 6.37, ~6.35 keys.
1 Sold for $11.72/ 2.33 = 5.03, ~5.05 keys.
Excluding all other sales due to them being either too low for current buy orders or too high for current sell orders. Going with 5.7 keys solid.