Bounty Boards: How to make them fair and make sense

So I wanted to create a new adventure hook I could use over many campaigns and figured, “Hmm, most medieval settings would have bounty boards set up in towns, offer prices for people willing to go out and deal with local problems”. Sooo I got out my Monster Manuel and Dungeon Masters Guide, and 2 hours searching online, and here’s my actual problem.

When sorted via challenge rating (DMG pg 136) monsters have their value set via the 5 different currencies which you roll to the d100 to determine which currency you reward players with. However, lets use Goblins (MM pg 165) and Kenku (MM pg 194)as the example. Both are CR 1/4, which places them on the Individual Treasure: Challenge 0-4. However, common sense would tell me the following:

Assume a town has a problem with Kenku and Goblins.

Kenku are known for their greed and will do anything to possess pretty things. While many beg, others steal or commit other crimes to earn such possessions. When you defeat a Kenku, it is logical to find gems, coins and possibly art objects in some form in its home whatever place it may be.

Goblins on the other hand are also motivated by greed, however their tendencies towards forming large groups or smaller packs prevents any 1 goblin from achieving a large amount for himself. However they have a tendency of training animals such as rats and wolves (or sometimes a Worg).

While a Kenku or even a group of kenku can cause quite the problem in a town, if there is a goblin problem, the town will often rather have the goblins taken care of over the Kenku. As such, on a Bounty Board a pair of goblin ears as proof would be worth more than a Kenku Beak as proof, despite them both being the same CR and belong to the same treasure Table.

So how can I make the Bounty Board both fair to the CR and make sense with the D&D Lore?