HelloCustomer Thank you for coming to Just Answer and allowing us to help you with your question. You don't have to have receipts if you use the IRS standard mileage for work use of your automobile. That means that you claim as a deduction 48.5 cents per mile driven for business use. The best way to prove this mileage is to keep a notebook in your car and writing down each business use, the date and the miles driven. Since you didn't do that, you need to find some other way to prove business use. Did you have a set route that you drove? Delivery drivers can prove that they had a route of x miles that they drove y number of days worked. Did you show houses? Can you prove from your appointment book which houses you showed on which days? Then you can go measure the mileage from your office to the houses and make a list of miles that way. Find a list of the houses that you showed and determine how far each house is from your office, then try to find a way to prove how many times you showed each house. Remember that commuting miles (from your home to your office and back) aren't deductible.
Hopefully these suggestions will help. Let me know if you need more information.