I could go into lengthy discusions on why this is different but Instead I will Make my point thusly:
Do you need a professional to help you buy a loaf of bread?
Do you need a profesional to help you pay your gas bill?
Do you need a professional to help you buy gas for your car?
Do you need a professional to help you pay salse tax when you purchase something at a store?
The reason Government taxes it's citizens is to proivde money to run the government; ask yourself why it has to be so complicated.
Depends on the amount of money. If I were spending 20-30% of my annual income on loaves of bread I would consult a purchasing expert with experience in bread. Likewise the other things you mentioned, including sales tax. If I were spending 30% of my money on sales tax, I'd be using planners like crazy on large purchases to both avoid incurring the tax and to look at methods to lower the taxable consideration.
The reason experts are hired is simple cost vs. benefits.