(taxpayer, commission seller, reported income of $3,307 and claimed business deductions of $17,000; shoebox of receipts provided to tax preparer and court noted it was unclear whether preparer made any attempt to distinguish deductible from non-deductible expenses; largest expense was for taxpayer's car; mileage log kept, but nothing more than odometer reading recorded in log with no information of where taxpayer drove, purpose of trip or business relationship to persons visited; log included 27 miles driven in daily work commute; taxpayer conceded that some personal trips included and presented no evidence of appointment books, calendars or maps of sales territories to corroborate log; deduction for mileage expenses denied in full for failure to satisfy substantiation requirements of I.R.C. Sec. 274(d) and court not permitted to estimate business mileage because I.R.C. Sec. 274(d) supersedes Cohan rule).