Dear Sanath Shetty,
If you do not have place of business in Delhi but you carry on the activity of buying and selling in Delhi, you are mandatorily required to obtain registration under Section 18 of the DVAT Act provided your transactions exceed or are likely to exceed ₹ 20 Lakh per year. Further, the tax under DVAT is to be paid by every dealer. Further, even if your transactions do not exceed ₹ 20 lakh per year, you may still obtain voluntary registration under DVAT so that you can take input tax credit on your purchases and deduct the same from your output tax. Please note that the definition of dealer specifically includes a casual trader and a casual trader is defined as "a person who, whether as principal, agent or in any other capacity undertakes occasional transactions in the nature of business involving buying, selling, supply or distribution of goods or conducting any exhibition-cum-sale in Delhi whether for cash, deferred payment, commission, remuneration or other valuable consideration". Therefore, depending upon your taxable quantum, you may decide whether to obtain registration and carry on the business in Delhi or to forego Input tax credit if it is only a one-off transaction with small amount of turnover. Of course, if you intend to obtain registration in Delhi, you need to obtain a business premises in Delhi.