Ask them what service they are using and if they know the speed. Some of the common services here are: Arnet (DSL), Speedy (DSL), Fibertel (Cable).
If you find the speed too slow when you get here, and the owner is agreeable, you can ask them to call and have the service upgraded while you rent. They, of course, may charge you for the price difference which is usually not a lot.
On a side note; Fibertel will do upgrades over the phone and on the spot. Today we upgraded from 3mbps to 6mbps for $39 pesos more a month. All it took was a 5 minute phone call, and now the speed difference is huge. Even though we only doubled, it seems to be bursting much higer than the 6mbps we signed for.