If you're a real entrepreneur and want to grow a startup business you'd serve yourself well to read Michele Prices recent SeNSE blog post "The 12 Reasons..."
As someone who's been in sales (and engineering and corporate education) for over 30 years I couldn't agree more with her premise that it's important to create an environment of mutual respect. Buyers, the folks you're interested in meeting, are really just suspects or prospects until you can confirm they really need your services or products and are willing to as Michele put it "play nice". Just because they will be paying you doesn't give them the right to be disrespectful, disingenuous or deliberately disagreeable! If you have any self-respect you wouldn't accept such behavior in a personal relationship so why would you in business? Oh, that's right, you think you have to or that it's ok because of the money. Wrong!!! Go find better clients or a new career if you find yourself continually willing to take that kind of abuse.
So how do you minimize or avoid it all together? By having excellent communication skills and an effective sales process that allows you to get both the prospect's and your own cards on the table right up front, so nobody gets hurt and you can disqualify the suspect early in the discussion so you don't waste much of your limited and precious time, or their's. Unless you own a "time machine" you won't ever get it back and as the saying goes, "time is money". A positive attitude is important, but it won't get you far if you keep making the same mistakes like getting caught in the "free consulting" trap set by many suspects.
Learn to identify good candidates for your service or product quickly by asking all the right questions, at the right time and in the right way. If their answers confirm they need or want what you sell and your companies are a good fit than continue in the process. If not, then cut your losses and go find a better prospect. Maintanin an abundance mentality and believe what your mom told you about "there's plenty more fish in the sea".
And don't forget to ask about their budget. There's not much that's more deflating than to spend two hours or two days working on a "hot prospect" only to find out they either haven't got the money to pay for it, or they believe you should do it for almost nothing! Also make sure you're speaking with the person who has the authority to spend the money, or that they are willing to get you in front of the decision maker(s) soon.
Having a good sales process you can trust and use consistently will help you maintain your own self-respect and turn your idea and entrepreneurial passion into more than just a non-profitable pipedream.