I know, you might think this practice is a little out there, but there are actually companies out there who will help you do it, as mentioned in INC Magazine’s Insider.
First is Task Rabbit, who does things you might not want to do, such as providing intel on a competitor. No idea what the fees are, but the example in INC cost $150, which isn’t much if the intel is good.
Second is Clubhouse, which will keep ongoing track of your rivals for you. Fees weren’t mentioned, but they’re probably proportionate to how much intel you want and how often you want it.
Third is Glassdoor, who does reviews on the competition, such as looking at their Yelp ratings, or Trustpilot. You could do this, but you run the risk of the target finding out who’s making inquiries about them. I’ve used both to research potential clients, and recommend them.
Fourth, you could go full monty and hire a private investigator if you really want a lengthly workup on a competitor. I would imagine you’d Google them.