I for one would like to know how someone who isn't properly paying their taxes would actually cost you money.
Customers can go with any photographer in Set (A). We'll call you (A1), and the rest (A2), (A3), ... (An). All customers belong to Set (B). Your income is based on members of (B), (B1), (B2), ... (Bn), who choose you over other members of Set (A).
It would be a lot easier to draw this out on a white board, but long story short is that whether or not any member of Set (A) is paying their taxes or not really doesn't matter, unless of course the customers in question are more worried about paying peanuts or less, in which case you aren't actually in a market.
In that case you're in a fantasy land where you think you have some kind of right that says you MUST make a profit, are entitled to profits, and that everyone must bow down and kiss your backside because you're just special. That isn't a real market, it is scraps that fools chase.
If someone undercuts you on price with the savings equal to the value of what should have been their taxes, then there is nothing that says those customers would actually have come to you anyway. There is no law that says I MUST hire a photographer. If I don't like the price of one, I can skip hiring that service and spend my money on something else I feel is more profitable for me.
I've never hired a photographer. Am I stealing what should rightfully be their money by not paying them for stuff I never hired them to do for me in the first place?
(I have spent a lot of time around successful business men and women. I have taken many classes on business, written dozens of business plans and proposals, and read a lot on the subject matter. Not once have I come across a single instance where someone said "And I own all my wealth and success to getting my competition charged with tax evasion or fraud".)
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