You’ll rarely be too early. If you’re building some people want/need, they will be happy to hear what you’re working towards and potentially give feedback.

If you have customers that are interested, and you end up burning the relationship, there are usually other customers that are interested. The real risk when founding a startup is that you end up building something nobody wants, because the need is made up. Once you have ~10 or so customers, you can be reasonably sure that there are more than 10 or so customers, because markets are almost never that small or that specialized.

(The exception is companies that are glorified consultancies, eg. you have just one customer that needs a very specific service done. But these are eliminated once you've triangulated enough to find 10 or so customers. At that point your product is general enough that it will no longer appeal to the companies that just want custom development outsourced.)

You can definitely do certain kinds of sales too early. Early sales should be website and brand creation, and talking to people about what you’re building to see if they’re interested, not necessarily closing deals. I’d say close 1 or 2 pilot deals (for pennies and/or free is good) and then pause it there, so that you have only a reasonable amount of pressure to build and steer a high quality product.

Otherwise you’ll be under such stress that you’ll become reactive and lose your Birds Eye View, and that’s a slow way to sink.

My flippant answer is ask Bill Gates about that. It seemed to work out.

But in reality, as long as you're somewhat honest in the sales process, it'll still work out better to talk to potential customers as early as possible. Maybe the dogma has changed, but doesn't YC say to talk to your early users/customers as early as possible, and if you dont have anyone like that to talk to, how are you even building this thing you have no connection to?