I've done a lot of interviewing for technical roles over the years. I wish I could say that I have never let a bullshitter through, but I reckon I've done quite well.
Some candidates have been complete fantasists. These characters are like the medical wannabies who lie their way into hospitals just for the thrill of performing operations, and basking in the imagined respect. Quite often, they have utterly convinced themselves of the truth of their fake training and experiences.
Other candidates have been deliberate fraudsters who want the money without the grief of the training and experience required to do the job properly. Occasionally they live the lie for so long that they begin to believe it themselves.
One meets candidates who actually have the experience, but without any aptitude whatsoever for the job. These have failed to keep up with their reading or training, and have no idea of the extent of their inadequacy.
For different reasons, all these candidates will present thmselves for technical interviw eagerly. Mostly, as the interview progresses they become aware of their inadequacy. Occasionally they don't and will tell their agent that they did really well.
The first trick in any technical interview is to understand what skills you really want. There is often a huge difference between the skills you think you need and the skills you really need.
The second trick is to ask questions that require an understanding of the technology rather than just getting them to spout facts. Human BOLs (Books on Legs) are useless for any real work It is not particularly just experience in a technology but an understanding of it that you want, and an ability to learn fast under pressure, and to know where to look for information.
The third trick is to have a series of simple questions where the answer would be known by anyone who had ever worked with the technology. As far as SQL Server goes, we all have our favourites but I'd never let slip, in a public forum, what they are!
The way of making ones life simple is to stop using any agency who presents a bullshitting candidate. This forces them to do all the screening, and CV checking beforehand. If they ask you what the technical questions are that they should ask, again you should use another agency. The word soon spreads amongst the agencies, and the bullshitters and fraudsters stop coming. This may sound tough but it is only forcing them to do the work they are supposed to do anyway, and for which they get paid handomely.