Key legal question
Whether the claimed expenses for the self-employed side activity were deductible as business-related costs.
Extracted holding
The claimed costs were not sufficiently substantiated and were disproportionate to the declared turnover; only a 20% lump-sum deduction was justified.
Extracted reasoning
A self-employed person must prove the expenses. Here the taxpayer did not document the costs adequately and did not account for private use, especially for telephone and office space. A 20% lump-sum, analogous to the rule for unsalaried secondary employment, was considered appropriate.