I fished in Ascension Bay near Punta Allen, about 2 hours south of Tulum two years ago in April. I stayed at the Cuzan Guest Lodge. It was fine for me, good guides, and food. The accomodations were about 2 steps above camping. We fished all around and caught bones, jacks, snook, baracuda, cubrera and mangrove snappers. I had two legitimate shots at permits, but could not get them to eat. I hooked two tarpon (15# size), but lost them both in the mangroves.
Most of the bones were caught on crazy charlies with bead and monfilament eyes. In the real shallow water the beads tended to get stuck in the sand. I ran out of mono eye charlies and ended up cutting the chain bead eyes off with my wire cutter. Sometimes the bright ones were what they wanted, many times a tan/brown with minimal body braid worked better.
Snook were caught on large red/orange flat wings (size2/0).
Tarpon were hooked on standard tarpon flies in drab colors, "cockroach" patterns were popular.
I would imagine the Tulum area would have some of the same species and the same flies would work.