Some useful questions to ask an SEO include:
- Can you show me examples of your previous work and share some success stories?
- Do you offer any online marketing services or advice to complement your organic search business?
- What kind of results do you expect to see, and in what timeframe? How do you measure your success?
- What's your experience in my industry?
- What's your experience in my country/city?
- What's your experience developing international sites?
- What are your most important SEO techniques?
- How long have you been in business?
- How can I expect to communicate with you? Will you share with me all the changes you make to my site, and provide detailed information about your recommendations and the reasoning behind them?