1. If you ask multiple questions in a reply to a customer, they will answer only one. Usually the last one. Sometimes the first one. Numbering your questions really helps.
2. The more questions you ask, the less info you get in return.
3. Spotting a "toxic" potential customer at the earliest will save you a ton of time & money. Evading a "toxic" potential customer is easy, just say "no" to a feature inquiry.
4. The cheaper your product is the more "toxic" customers it attracts. I can't even imagine the amount of "toxicness" software companies face in the $0.99-apps space.
By the way, that is why our helpdesk app is priced the way it is. We are cheap, but "reversed cheap" - meaning our top pricing plans are very VERY affordable ($249/month for unlimited agents, storage, everything) compared to our competitors, but it gets more expensive with our lowest plans. Like, the 1-person "freelancer" plan is $29/month, while most of our competitors are priced somewhere at $1/month (or even free).
5. Customer support is cheap marketing. Be amazing. It's not that hard - keep the response times as low as possible and amaze a potential customer with "support stunts". Like "do you have a feature X?" - "no, but you know what, I thought it's a great idea to have it, so we just spent 20 minutes to add it and now we have it"
Real world example: a customer asked us if we we have a calendar view of the tickets' "due dates". It took me 15 minutes to find a good js-component, while Max was already hacking the JSON-backend for it. Then we glued it all together and another 20 minutes later the customer was enjoying the feature. Oh, and it is now one of the top used features in the app.
6. Every time you're answering a support question - ask yourself, if the answer can be published to the Knowledge-base (by the way, we have a super-easy way to do that in our app, just click "publish to KB" after replying to a ticket). Not only this is good for your customers, it's also very good for SEO. See, when you're replying to a support ticket - you're creating content anyway. Why not publish it online (removing all the personal/sensitive details of course)? Google loves content!
7. When someone sends you a "feature checklist" to fill - usually they just want you to do their job. They simply forwarded the checklist from their boss - so they don't have to waste their time reading your website. I'm not telling you to ignore them, just so you know.
8. Your existing customers are way more important then the prospects. Especially in a SaaS business, where you might end up trying to outrun churn with your marketing.
9. Support by founders and developers - rocks.
10. Support people have to be invited to all product meetings. Sales people - not so much (and do you even need sales people? ok, I'll shut up)