Probably the easiest way to hire a guide would be through your hotel, but the profits don't necessarily go to your local guide or her village people. We decided to book through Sapa Sisters, since 100% of the money went to the guide, a local Black Hmong woman. It was a little pricey at $28 per person, but the money went to the right place and our guide ended up being really great. We also got a van ride back at the end of the hike, since the hikes are not in loops. This was great, because it allows you to see a lot more without having to double back.
We walked by Cat Cat Village (though we didn't see the heart of the village), Lao Chai Village (where we ate lunch), and Ta Van Village (where our guide is from). We encountered lots of farm animals along the way - water buffalo, pigs, ducks, and more. For lunch we had a hearty plate of fried noodles (two of us got a plate of fired rice instead). We had a view of the little river in the valley and offered us a much appreciated break from the heat. It was in the low 70s but the sun and the humidity made it feel much hotter (definitely apply sunscreen!). I used deet and, thankfully, I didn't get any mosquito bites. Overall, the trek was amazing and the best way to learn about the area and see the scenery!