There is no question about it, a Merida house hunt is a heady experience. Some approach it methodically, renting for six months to a year (or even longer) in an attempt to be sure that they have the right city and the right neighborhood. Others come for the first time on vacation and leave with a purchase contract. We fell somewhere in the middle, deciding to buy on our first trip but looking at multiple properties over the course of nearly a full year before we settled on ours. There is no right or wrong way...you just have to do what feels comfortable for you personally.
Others have posted good advice that was helpful to us, and so we thought that we would add a few of our own lessons to hopefully pay it forward and assist people who are starting their search now.
Your long term plans may influence where you buy.
Be realistic about how you will live in Merida.
But it is unlikely that you will become a whole different person, so be realistic about what is important to you. Some people would never be comfortable as the only expat on their block, and some will not be comfortable with anything less. Are you best suited to the middle of Centro (the primary tourist district), the edges (which are more local), or the northern suburbs like Garcia Ginares or Colonia Mexico (closer to shopping, Starbucks, and some great new restaurants)?
There is no question that life in Centro can be noisy, with frequent celebrations, fireworks, and lots and lots of buses. There is a reason why realtors note that a property is "on a non-bus street." It is worth visiting a target property at different times and on different days to see just how busy your potential new block might be. We didn't realize until a third visit that a property that we really liked only seemed quiet because our first two visits were on the weekend.
Take lots of pictures, notes, and measurements.
They are not about to run out of houses in Centro.
Our own hunt was full of ups and downs, excitement and disappointment. But truth be told, I already miss the experience a little bit. So take your time until you find just the right place (and the right price) that works for you.