Preapproval... What if bank statements and tax return don't match

[Bryan T.]

I have never purchased a home before so I am wondering if the conventional mortgage preapproval process is similar to an IRS audit. 

For the preapproval, what if bank statements and tax returns don't match? Do they check for accuracy when you send them your tax returns and bank statements? Will they ask you to classify every deposit and withdrawal found in your bank statements? What if you accidentally under reported any sources of income or accidentally over-calculated any expenses on your tax returns? What if you sometimes deposit money that you get as gifts from family?

I am just wondering if the preapproval process is basically like an IRS audit where they check every tiny detail. If it is I am sure that many people will have tax returns and bank statements that don't match perfectly right? 

Also, let's say you have $1,000,000 in the bank right now (that you saved up over many years) but make $100k a year. Will they want to know exactly where the $1,000,000 came from or what?