What proof of expertise do UK immigration accept for conference speakers?

This question is a followon from What are the visa rules for US speakers, at UK conferences, who may be getting paid?

Let us assume the following givens:

• a person would normally be admitted on arrival to the UK if visiting as a tourist (specifics in this case: a Canadian citizen with strong ties to Canada)
• a person is both attending and speaking at a conference that is not run by a university, but also not run as a profit-making enterprise (examples relevant to me include ACCU and NDC London.) Admission is charged to these conferences
• the speaker has been offered airfare, hotel (perhaps not even for the entire length of the conference), and conference admission, but not meals, incidentals, or an honorarium to cover these
• the speaker is not running a lucrative workshop or precon to bring in revenue that approximates their daily bill rate, nor visiting consulting clients and billing a day or so, nor anything else that would make the time spent in the UK "billable time".

The advice from the UK government says that all visitors may

5 A visitor may: (a) attend meetings, conferences, seminars, interviews; (b) give a one-off or short series of talks and speeches provided these are not organised as commercial events and will not make a profit for the organiser;

Setting aside the issue of whether these conferences meet the "provided" clause, there is some suggestion in the other question that it would be helpful if the immigration office understood that the applicant was an expert in the field, and recognized as such the world over. OK. How can I show that?

I have read elsewhere that a letter from your employer is a good idea. My employer is a company with two shares. I own one and my husband owns the other. If I was an immigration officer, a letter from the applicant or the applicant's husband would be worse than useless in establishing expertise. I know many of my fellow speakers are in a similar situation - we barely have employers in the usual sense, or our speaking is a side activity that our "day job" doesn't know much about.

I would like to think that the mere fact of having your talk accepted at the conference in question would suffice as proof of expertise. Would printing the "speakers" page be useful? Or the "congratulations we have accepted your talk" email? Should speakers request a letter from the conference specifically for the purpose of showing immigration what an expert they are? What would be good wording for that letter?

Others have said, in other contexts, that you should invite the officer to "google me". This seems insanely arrogant and I note that only men have claimed they would do this. I don't believe I could say it with a straight face. Is it actually good advice?