Starting a real estate business in Spain can be a lucrative venture, but it requires careful planning and preparation. Here are the steps you can follow to open a real estate business in Spain:

1. Research the market: Before starting your real estate business, research the market to understand the current demand and competition. Study the local real estate market, including property prices, types of properties, and areas of high demand.

2. Obtain a license: In Spain, a real estate license is required to operate a real estate business. You can obtain a license by completing a training program and passing a qualifying exam.

3. Register your business: Register your real estate business as a limited liability company (S.L.) or a self-employed individual (autónomo). You will need to register with the Spanish Tax Office and obtain a tax identification number (NIF).

4. Obtain insurance: Obtain liability insurance to protect yourself and your business in case of lawsuits or accidents.

5. Build your network: Build relationships with other real estate professionals, including real estate agents, mortgage brokers, and property inspectors.

6. Develop a marketing plan: Develop a marketing plan to promote your business and reach potential clients. This can include a website, social media presence, online advertising, and networking with other real estate professionals.

By following these steps, you can successfully open a real estate business in Spain and start building your client base. However, it is important to be aware of the local regulations and requirements, and to seek legal and financial advice as needed.