It's a topic that has gotten some traction recently, but it warrants even more: Polls in Mexico are unfortunately often very unreliable, and purposely so: Rather than to present a snapshot of public opinion, the figures are "massaged" to present one candidate or party in a good (or bad) light. Pollsters - not all, but many - are unfortunately for sale.
Yes, some candidates take it too far, questioning any and all polls and refuse to rectify a failing strategy (think AMLO 2006). But many have a reason to do so, and perhaps AMLO more than many others these days:
Francisco Abundis, head of Parametría, warned that parties will try to use any data the coming weeks in particular to suggest that that the presidential contest is getting narrower, and that AMLO is not growing in the polls. The step is then very short to specifically ask polling companies for "results" - give us something that backs however we want things to be.
Abundis' advice strikes me as very sound: Take polls with more than a pinch of salt, and look for patterns across various polls and across companies, and over time.