IMO it is a mistake to assume that reputation needs to be linked to an identity. I believe that reputation will be earned and sold.

how does reputation maintain value without being linked to an identity?

If maintaining the reputation is worth more than burning it (by exploiting trust, etc.) then it can maintain value.
Businesses/brands change ownership, and the reputation transfers with it. Often users/consumers don't know or care about changes of ownership.

but isn't the brand the identity?

think it's reasonable to bet that reputation can be earned and sold but imo identity is the vehicle for that

reputation maintains value only in context of the originating identity.

people farm and sell video game accounts all day but once you discover that an account was purchased, you are immediately less impressed

Would you be more or less impressed if new owner bought the reputation for 5k? 10k? 100k? 1M?

a writer by passion, a developer by curiosity, a product guy by necessity  - lesgreys.com, /grey

it becomes two things:

1. as soon as we know that reputations are commonly bought and sold, they lose meaning
2. if it transacted for $1M, the fact that the owner has $1M to buy something like that forms its own reputation