After having issues over the years with new bandmates, I've been considering having a 90 day probationary period before someone is in the band permanently. Past problems were stuff like the new guy wanting to take over and run everything, basically just being an ******* once he was hired. Or the guy just wasn't as good as you first thought, playing the same solo on every damn song, terrible feel or no feel at all for what the band is playing. Different goals become apparent soon after joining. Has anyone done this before?
When I joined my current band, they gave me two gigs, or about three weeks from my first audition, to "try out" along the lines you're talking about. Just one gig is too easily a fluke, good or bad, but stringing someone along for too long tends to create bad blood if you do need to let him go; the longer a guy plays for you, the more other opportunities he's had to pass up to pursue this one, so if you let him go two months and a dozen gigs into this thing, you're likely leaving him to twist in the wind after he's turned down other paying work. In my case I nailed the first gig, the second one was a little rougher but I held it down. They conferenced, and the drummer came up to me and said "if you want the gig, it's yours." We've done many more gigs since then.
I will say that "permanent" is a highly fraught term when talking about practically any employment, because it's never really true. Regardless of tenure, if my guitarist no-calls no-shows to a gig and doesn't have a
really good reason (like "I was heading there, got T-boned by a drunk driver and woke up in the hospital the next day"), they're gone. Seriously, do you want to be left high and dry like that
twice? So, you can call a guy "permanent" as soon as he's your week-in, week-out player on that instrument/part. But really, whether he's a month or a decade into it, he's as permanent as his willingness and ability to be a reliable, professional member of the group. Nobody's truly indispensable, especially in the bar band scene.
On a related note, I will also say that a formal probationary period, aka "rookie" or "pledge" status, is a double-edged sword. In the corporate world, it gives you firmer ground to let a guy go for lesser or fewer transgressions, but corporate or personal, the kind of loyalty and professionalism that "you screw up just a little and you're out" tends to produce is skin-deep and fleeting. The
true test, IMO, is when you let him be himself; that typically happens a few weeks past any "tryout" period, explicit or implied. Once he's comfortable in his new position and with the band's existing interpersonal dynamic, does he still show up on time and ready to play? Is he still doing his homework? Does he still treat everyone else with the respect he's given? If so, you've found your guy. If not, then "rookie" or not, it should be at least worth talking to him about what expectations he isn't living up to before you give him the boot (assuming the expectation isn't something so boneheadedly simple as "show up to the gig").