Interesting question, but I don't really see it as a "chicken and egg" type challenge.
For a service startup business, you will still need an online presence. In the Lean Startup method we talk about MVP, the minimal viable product you can build to both test the waters and get paid. Why build a business that no one wants and therefore, no one will pay to use?
So, a better approach would be to test the waters first with a few phone calls. Is there a need? Want to be sure? Make one hundred calls. Then let's talk.
There are affordable ways to build a MVP.
The examples you have given are dependent upon having users in the area (others date around you, others to do your tasks that live nearby, etc.). These startups find an initial group of users in localized markets before expanding to other locations, usually offering an option to be notified when there are enough users in your area for the launch. The userbase does not have to be huge, just enough to fine tune results and offer concrete data "We tested our dating app in Cambridge, MA and 25% of test users went on a date in the first month. Users tended to click on the interests section the most, so we made that the highlighted section of a profile..."
Take an example like TaskRabbit. Using Jeff's suggestion that you start manually, I would suggest:
1) Start providing the services yourself by advertising your ability.
2) Grow the business to a point where it makes sense to have a technology solution as an intermediary because it's getting too hard to manage yourself.
Not only do you validate the need with the customer, but you've figured out how to make money in the process.
Totally agree with Jeff as well. I have been scaling software as a service product for the past 10 years and most experts will agree with me when I say that you need to get to 100 paying clients before you can really say you have a your MVP as Jeef explained (i.e. that has market value and fair potential).
Where do you start? By getting the first 10
Right now, as you are probably experiencing already, it is all about hustling, talking to ideal customers, showing your product, getting their feedback, implementing their ideas into your MVP, and doing this over and over until you get to 10 paying clients. Then you can start growth hacking and content marketing activities based on this early success.
Also, selling over the phone is great, but if you can meet these customers face to face, that's even better. You can't really build a relationship over the phone, at least not as good as in person. This step will help you build champions/ brand ambassadors, that will hopefully spread the word about your product, give you great testimonial, and agree to a case study (maybe a video one next time you meet them in person)
Nobody wants to be a guinea pig and most buyers will want to see demonstrated value before buying a newish product/service. Use these early customers as your social proof, and let their success stories do the selling for you.
Not sure about your price point, or even if you have a SaaS product. If you tell me more I can give you some quick metrics and pointers to help you along the way.
Best of luck!