I'm in Canada, I have had clients audited/reviewed by the CRA(Canadian equivalent of the IRS) and I can tell you there is no "fudge factor". They cycle their reviews based on industry, geographic location, inconsistency with other related returns, and use other risk factors to determine if you are a target for review.

I'm also a professional accountant, I agree. People are confusing accountants with bookkeepers and assume that everybody has a simple tax situation and can do their own taxes. While there are strides to make bookkeeping automated there are still a lot of moving pieces that need to be in place. Notably I often have to sit down with clients to discuss what is and what isn't allowable. Often the two receipts could look identical but only after discussion you find that one is personal and the other is for business. The automated bookkeeping solutions are definitely a garbage in - garbage out situation. Another side of the profession is auditing. I use a lot of automated tools and perform a lot of data analysis which is certainly more efficient and effective, but I still need eyes-on to observe for many of my audit procedures. Again, there is a lot of discussion and professional judgement that takes place during an audit that simply couldn't be automated with today's technology at least.