would there be a way to try out a new hire for a 'trial period', maybe on like a 3-month starter project paired with someone more senior? then after the new hire has proven him/herself over those months, a formal offer could be made.
There are ways to do that, but there are a lot of complications.
First, most truly good workers, especially in the tech industry, aren't sitting idle for a long time, so they are often either being hired away from a job they already hold and possibly being asked to relocate. A lot of those good people will not make a commitment like that to you and disrupt their lives if you aren't ready to make something of a commitment to them. So, this might work well for entry level positions but probably less so for senior people.
Then there is the cost of dealing with them for three months or until you figure out if they are right. While this is much less expensive than keeping the wrong person on for a long time, it is still very expensive. Most managers want to try very hard to find the right person the first time not go through a whole series of short term hires looking for the right person.
In some situations this is a great idea (and what many companies actually do), but there are many occasions it is impractical.
When I started at my current (also first post-college) job, I was a contractor for about 8 months before becoming a regular employee. Two of my coworkers have made the same contractor->FTE transition. When I started it was explicitly a contract-to-hire position... for whatever reason we apparently don't do that any more, although our latest full-time position was first offered to some of the current contractors before our boss started giving us resumes to look at.
I could definitely see this reducing the applicant pool, although a surprising number of people have been looking for hotels on their first day, and then live here during the week and drive several hours home on the weekends.
