Validating with "pre-ordering", is it really fool-proof?

Many founders suggest that instead of building the actual product you should validate people "willingness to pay" by presenting your idea (may be with some screenshots) and ask them to pre-order. If you get a good response, you can now start developing the actual product.

My concern with this approach is that most of the people (including me) would be uncomfortable with pre-ordering but they would happily buy the solution if they can actually try the product.

If we use this pre-order approach for validating viability of an idea we are ignoring these people (since they won't pay upfront) and relying only on a small subset (i.e. people who are willing to pre-order) to verify viability of our idea/product.

Is it really a fool-proof approach always? My assumption is that, it has a great chance of giving you a false result especially when you are reaching out to a small list of people.

For example, if you've your product already built (ideally an MVP) and you may get 2 customers our of each 100 leads (i.e. 2% conversion rate). On the other hand, in case of pre-ordering, you might have to reach 200 people to find a single buyer (i.e. 0.5% pre-order conversion rate). If you reach only 100 people and no one pre-orders, should you drop your idea?