Double taxation & New Mexico Gross receipts tax

Why am I paying taxes twice on the same income?

You are not actually paying taxes twice on the same income. Income taxes and gross receipts taxes are different tax programs. Income tax is paid on the profit a business earns; gross receipts tax is paid on the sale amount. Read the Taxes self-employed people pay.

I earn commissions on sales on which the company I represent pays GRT. Aren't taxes collected on them twice?

Commissions involve 2 separate transactions which may be subject to gross receipts tax. First is the sale of a product or service on which the seller must determine whether the sale is taxable. Second there is the commission paid to the sales representative for facilitating the sale. Note: If the sale is not taxable, then the commission is also not taxable.