How to evaluate meditation centers is a tricky question as there isn't any kind of regulatory body or professional certification for these retreats. There's a vast array of different forms of meditation and styles of teaching out there.
If you are looking for centers that are more aligned with insight/mindfulness meditation then the Buddhist Insight Network has a searchable database.
If planning to do a retreat with an insight teacher, try searching dharmaseed.org for their talks and listening to their approach/style to see if it feels like a "fit."
Our general advice in relation to any meditation center is to try to find out what style or approach they have regarding lineage or tradition, is it a non-profit or for-profit, how much training do the main teachers have, where from, and with whom. Doing a Google search if anything doesn't seem quite right is a good idea because these days a lot of info is available online regarding ethical misconduct in relation to particular teachers.