Things to look for when hiring a maid / cleaning service

I've never had a house cleaner before but I'm open to the idea of hiring one. The thought of letting a stranger into your house is a bit scary though, especially for multiple hours when you're not home.

I'm not sure what's customary when hiring a maid / cleaning service, and I wanted to ask here if anyone had tips for me? Some of the questions that come to mind are:
  • Do you have the maid come over for an interview, or do you only do that virtually?
  • How acceptable is it to turn down a maid after an interview? Should you interview multiple and choose between them, or pick one and only turn them down if there's a big red flag?
  • What's the best way to ask for references, especially for a lot of freelance maids that won't have a Yelp / Google reviews page?
  • When discussing pay, how mush should I budget for a tip on top of the regular pay?

Re: Things to look for when hiring a maid / cleaning service

When my roommates and I were thinking about hiring a maid, we chose to go with the maid that had been cleaning the apartment above ours. She came recommended by the family that lives upstairs and they've trusted her for years. We felt pretty safe hiring her because we knew the family upstairs had nicer stuff than our apartment, and we knew she wouldn't do something to sabotage her relationship with both apartments.

We invited her over, it was a chance for us to interview / get to know her / ask our questions, and an opportunity for her to see our place, understand which room s we wanted cleaned, and give us a quote. She ended up giving us a quote (I believe it was 5hrs cleaning for $150 the first time, with 3hrs cleaning for $90 thereafter). We thought it was reasonable to charge for the time spent cleaning, and thought it was reasonable that she spends 3 hours at it.

You could tell she knew what she was looking for when she examined our apartment (i.e., she opened the oven to take a look inside, since she was going to clean out the inside). That reassured me that we were hiring someone with experience.