They could recruit their experts from the community itself, limited to those over a certain karma threshold, adding further incentive to participate.
And it had better not be implemented as one of those stupid unsolicited pop-up chat windows.
> As a registered user, your reputation on the site is a part of your identity on the site. It reflects, to an extent, your familiarity with the site, the amount of subject matter expertise you have and the level of respect your peers have for you.
http://meta.stackoverflow.com/a/7238/150097
In addition to that, it is possible to write well written, but highly specialized answers that gain few upvotes, or relatively simple answers that accrue large number of upvotes simply because it is a common question. In this sense, reputation is a measure of how 'valuable' your contribution to the site is, which is often, but not always aligned with how knowledgeable you are. There are other outliers too, like answers that get featured on Proggit or HN, but those are far less common.
(It also used to be possible to gain large amount of reputation by simply being the first to reply to a poll with a popular answer, but those type of questions are no longer acceptable).
http://data.stackexchange.com/stackoverflow/query/105837/how...
Sure there are a few questions with highly voted up answers because they are widely useful, but there is certainly the minority of high rep earners. Even the new people who are gaining lots of rep are doing it by answering hundreds of questions.
I'd say that counts as an expert.