Client's name may appear in the description or in feedback. If so, use it. I'm more interested in identifying the client's company. If I can do so, I'll ask "It appears that you are Suhaib's cupcake shop and hand-held nuclear weapons company. Please verify."
Most important is identifying the client's industry. I'm most comfortable replying when I know the industry, because then I know whether I'm likely to succeed in resolving the issue or meeting the need.
Petra's "Hi" works well. If I know enough, I'll use "Manufacturer" or "Entrepreneur" as the greeting. Othewise, I skip the greeting.
You can choose to decline any job offers from this particular client or not submit any proposal. You are not obliged to accept any offers or submit proposals to all jobs. Let us know if you have other questions, we're here to help. Thanks!