I was going to suggest looking at reviews but one prominent and notorious strata manager has been soliciting reviews from their happy customers, asking unhappy customers to take their reviews down, threatening the owners behind negative reviews with defamation action (not possible) and flooding the review pages with remarkably similar five-star reviews. It’s easy to spot the fakes because they almost always reflect whatever the company’s main selling points are in their advertising. E.g. if the company promises “prompt and personal service” and that phrase turns up in a review, you can lay odds that the review was generated by an office junior on their tea break or AI.
On the other hand, people are more likely to post reviews when they are annoyed or disappointed, which tilts the balance to the negative side. If an indication of a strata manager’s success is that their clients are happy and contented, then they are less likely to get any reviews.
In your situation, I would call the companies you’re looking at, ask them if they manage many or any properties like yours and then ask if they can put you in touch with an existing client for a reference.
One other consideration is that the strata management company is only as good as the strata manager that they appoint to your property. You can have good manager working for bad companies and vice versa. What you need to be wary of are companies with a permanently toxic culture or who will offer you bargain basement rates that they will then more than compensate for with inflated Schedule B charges.