As a new salesperson, you could never imagine turning down work. But as your career develops, you may decide that taking on a particular client is a bad move. Here are some times to say "no" or to refer the business to a colleague:
You are entering uncharted territory. It is tempting to learn a new industry or skill set, but practicing on a real client is a bad idea.
The ROI (return on your investment) looks poor. If you can foresee that you will not be adequately compensated for your time and energy, say "no."
The project sounds too good to be true. That's because it probably is - particularly if you know nothing about the client or are taking the project because of the promise of future work.
The client wants everything done tomorrow. When time demands are unrealistic, you have little chance of pleasing the client - ever. Also, beware when you are asked to hire additional people quickly.
Your only reason for taking the job is that it will look good on your client list. This can be backfire. When the job is undoable and unprofitable, you will either "fire" the client before the job is finished, or you will get a bad reputation with an unhappy high-profile customer.
The client feels wrong to you. Trust your gut. If you are mismatched, or if taking this job will mean you can't take other work, you will regret your decision.