Why, when I'm looking for records in the late 1700's (and I have put in the dates), do I get records in the mid 1900's? This is entirely illogical.
It's because the search terms are not filters, but sort keys. The closer a record matches your search terms, the higher up on the list it will be. If there's nothing particularly close, then the way-off ones will be near the top.
Another reason the results can look illogical is that different search terms are weighted differently. For example, an exactly-matching name but wrong date will sort higher than a vaguely-similar name but exactly correct date.
You can filter searches, but they apply after a search has already been done, so filters are not on the main search page, only on the results page. On the current interface, they're on the left, below the Update and Reset buttons. On the new interface (currently under limited roll-out), they're a line of grey buttons above the search results.
It often takes a some adjusting of the search criteria before you can narrow down to the desired results.
Look at the example at https://www.familysearch.org/search/record/results?exactSearching=true&q.anyDate.from=1780&q.anyDate.to=1790&q.anyPlace=yorkshire&q.anyPlace.exact=on&q.birthLikePlace=yorkshire%2A&q.birthLikePlace.exact=on&q.givenName=George&q.givenName.exact=on&q.surname=fawcett&q.surname.exact=on. I have (from an initial list of around 1900 results) cut this to just 18 - by using an "Exact" option on the 1780-1790 birth of George Fawcett. If I want to cut-out the census ones, I can filter on "Collection" at the top of the page, so just sources from Births / Christenings collections are shown. See https://www.familysearch.org/search/record/results?exactSearching=true&q.anyDate.from=1780&q.anyDate.to=1790&q.anyPlace=yorkshire&q.anyPlace.exact=on&q.birthLikePlace=yorkshire%2A&q.birthLikePlace.exact=on&q.givenName=George&q.givenName.exact=on&q.surname=fawcett&q.surname.exact=on&f.collectionType=6
Any initial search probably will produce unwanted items, but with careful use of filtering, and by checking fields with the "Exact" option, you can usually produce a list to suit your requirements.
When you run into a problem like this, if you copy the URL at the top of the search result page and post it, like Paul has done in his examples, people can look at exactly what you see and help determine if it is a problem with your search or a problem with the search algorithm.
If it is a problem with the search algorithm, the people in charge of that need specific examples, best given as URLs, so that they can trace through the algorithm and see what is going wrong. Without examples they can't.
There does seem to be an increasing number of people complaining that search results don't seem to make sense. I have to wonder if something was updated in the algorithm that actually broke it.