Most people won't be faced with the dilemma of trying to purchase a house that isn't for sale, but the number could be higher. There are plenty of people who buy houses where they settled based on what was currently available. Maybe they really wanted an extra bedroom, an extra garage, more closets or even 9' ceilings, but decided to live without certain features because they could find one house that had them all. If the feature can be added/changed at a later date, such as different types of counter tops, or remodeling a bathroom, then setting for not having it may be acceptable. However, when the types of features that are missing could be costly or impossible to add, that is when settling becomes more difficult.
If the buyer had a savvy real estate agent they might have proposed looking at houses that are not on the market that best match their wish list and approach the owner about interest in selling. It doesn't guarantee finding the dream house, but it does expand the pool of possibilities.
There are a few things to consider before committing to this course of action.
The process is more time consuming. Unlike houses that are currently on the market, there isn't a database you can search. Finding houses that match your wish list will be solely based on the real estate agent's knowledge of the communities in the area(s) you are interested in living within. With this knowledge they can drive neighborhoods to find the obvious, external features on your list, like the number of garages, number of acres, and style of house. With this list they can do research to investigate the inside features. Ultimately they can provide a final "short list" of properties where the owners can be approached.
Because there isn't a quick database to search and because there is a lot more legwork to be performed the time it takes to find a house that matches your vision AND where the owner is actually willing to sell will likely take much longer than the typical house buying process.
Don't let this discourage you from attempting it. If you are not in a hurry and are very particular about what you want, give it a shot.
Let's say you've actually found a house you are really interested in. Now it is time to approach the owner. This can seem daunting, but it doesn't have to be. As with any proposition you present someone with, you don't always have to accept the first "no". Sometimes it takes the person time to work through what you have suggested and decide that they really mean "yes". However, you should know when the owner is sincere about their rejection, be willing to walk away and start looking for the next perfect house.
When you approach the owner, here are some points you might want to consider.
Don't be afraid to simply knock on the door and strike up a conversation. Your interest and sincerity can be expressed more with face-to-face interaction.
Don't beat around the bush. You may feel that if you can get them to like you first they would be more willing to say "yes", but they aren't going to answer the door to a perfect stranger and take time to get to know them before getting impatient about why you are there. Start with a simple pleasantry but then get to the point.
Be honest. People can usually sense it when someone is being dishonest or hiding something.
You are not trying to convince someone to sell their house when they have no desire to. But it never hurts to add some subtle suggestions to your conversation... ideas that remind them about thoughts they may have previously had about moving. These might include:
moving closer to work or family
moving into a smaller, more manageable house (they are aging or children have all moved out)
moving into a larger house to fit a growing family
need to reduce financial obligations
could use the additional money from a house sale
is this their dream home? are they ready to look for it?
If you get the sense that someone is on the fence, be patient. Thank them for their time and ask if you can follow up with them after a few weeks or a few months to see if they have changed their mind. Sometimes it just takes a while of processing the thought for a desire to take action to manifest.
Leave them with your information in case they do change their mind. Life may introduce them with a desire or need to move after your conversation and I can guarantee that if they have your information you will likely be their first phone call. Why go through the process of casting a net when a fish is already trying to jump into the boat!
Don't try to do this on your own. Make sure you have a qualified buyer's agent at your side to help guide you and to do the heavy lifting once you find a willing seller.
There are no guarantees that you will get your dream home this way, but as with anything in life, if you never make an effort your only guarantee is failure.