Competing with dodgy accountants

I was speaking to one of my clients recently, a one-man consultancy business in the contruction industry.  He told me that when he speaks to colleagues, they take a much more aggressive attitude to their tax affairs - in fact so aggressive that I would call it illegal.  The implication was that my client was "a bit soft" for not bending/breaking the rules and claiming for expenditure such as suits, and non-business expenditure that they might be able to get away with.  It also seems apparent that their accountants are either complicit or turn a blind eye to this activity.

Has anyone else come across dodgy competition?  Personally, it seems a no-brainer to me that I would stop acting for any client who I thought was involved in tax evasion and reporting obligations would also be met.  But I'm wondering if there is quite a booming trade for accountants who draw the line in a slightly different place to me?