It may be... for starters, if the open source developer is hired by a corporation although then the corporation is customer rather than user.

On more global and independent scale is also possible, but involves those who care to pay the developer(s) so developer(s) have incentive besides usual such as scratching itch etc. Given parent is talking about customer one may assume he meant paying customer. A bounty hunt program has potency for viable ecosystem.

Also, I believe when developer is helped in other aspects such as translation and artwork, it feels less like their solo project and feels like getting help therefore more open to suggestions whereas if its only negative criticism or bad bug reports attitude may be something like 'this isn't fun anymore...' although not everyone gives same value to this.

Oh well, bounty system was discussed before...