Step 4 in Market Research: Quotas - how many people of a particular type do I need?

We continue to explore the how to go about market research. 
Now we have established 1) who we want to talk to (Target Audience), 2) how many people to talk to (Sample Size) and 3) what questions to ask (Survey Questions).  Now, what if we need a certain number of respondents of a particular type?

Think about quotas - have a think about how you plan to segment the data. If you are running a survey on, say, banks, do you need a significant number of respondents who use each of them? If so, bear in mind that it will be easier to find NatWest customers than those of Coutts. So - even though just about everyone has a bank account - we could end up in a position where we are rejecting 200 starters for every complete. Sometimes it is better for timing and budget if we accept that some objectives are just not sensible.