When someone is paying you for your service you don't give them sarcastic replies. If you paid someone to mow your lawn and they missed a spot, you'd tell them to fix it. If you're the guy mowing the lawn, you're not going to be snarky and tell them to deal with it or say "I'll get around to it". It really is basic principles of business. Now, I took no offense when reading it myself; but I do see the unprofessionalism in the statement.