These days it’s been a dilemma for designers whether to proceed with this kind of requests or not but in my personal opinion, IT SHOULD NOT! This kind of requests are termed as SPEC Work, it is the work produced on speculative basis.
One of a fellow designer Jacob Cass has nicely articulated this in a real life example:
“I went for a dental check-up yesterday. After the dentist inspected my teeth, she suggested some work to prevent further tooth decay. I told her to go ahead, and if the dental work was satisfactory, I’d be more than happy to pay. She responded that she wouldn’t be able to do that, because she normally provides a service when a fee is agreed upon up-front. I said I’d let her know after I checked in with other local dentists.”
I think the above example clears the picture very much why clients shouldn’t come to the designer without paying him/her for the time he/she spends on their project. When a designer is assigned a job, he puts his time and efforts to it which should be compensated in return. It is always a good practice to decide the cost beforehand and get some initial payment (unless you have a very good trust on the client).