If an entrepreneur is asking you customer development questions, or getting feedback on their product, Don’t be nice to entrepreneurs if you don’t mean it! Give them honest feedback so they can improve their offering or move on to higher value project if needed.
You think you’re being nice by being supportive and complimentary, but in reality, you’re just encouraging them to pursue something that may not be viable.
It’s hard to be “mean” and disagree, but in reality, you’re being nice. Any good entrepreneur will want feedback so they can iterate accordingly and not spend time and money on something that’s not viable.
Don’t say “let me see the prototype when you’re done,” or “adding feature x sounds great” if you know you still wouldn’t buy it.
Bottom line: if you’re a potential customer of an entrepreneur and he/she asks you for feedback, give honest feedback!
Note: outside of customer development you should be extremely nice to entrepreneurs because they rock