I just saw an ad for a national tax return preparation company. They were offering a free review of your past returns for an accuracy check. Now I personally find this hysterical, because of the fact that every, and I mean every return from this company that I have reviewed in the past has had significant errors.
Now when you treat a tax return as a commodity and do not want the people to leave without selling them your product you do the return even if you know that the return is incorrect because of missing information. That is assuming that the preparer knows that the information is missing.
In my office if the information is missing we request it, from the client or at times from the vendor (financial adviser, other tax preparers, banks) or we are able to locate it on the internet.
We also talk through all major events for the past year with our clients, on those rare occasions where we have not already been in contact with them during the year (we encourage clients to contact us before any major decision to see if we can assist), to find out about any changes in their lives. We also work with them on planning for the next year as well.
So when we do start working with a new client, we request a copy of the last two years worth of tax returns. We are looking for accuracy on the returns, but we are also looking to verify that we have all of the information to prepare this years return(s).
Oh, the main reason for errors on the others returns is property taxes. People bring in the tax bill that is due in the first quarter as the tax bill for the prior year since it comes in at the same time as the rest of the tax information. We typically then need to look up the property tax payment history to verify that everything is current and what is deductible.