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

Yes, you could frame it like that, and say that identity can be transferred, and reputation with it.