You just cleared customs, and the guard informs you that you cannot take your luggage cart beyond this point. What do you do? You hire a luggage valet. These guys can haul literally hundreds of pounds of luggage, and they will escort you anywhere you need to go within the airport. Think of them as your personal human airport GPS system with muscles.
The tip amount is up to you. Keep in mind what you would pay for a luggage cart with no GPS system at a US airport ($4 USD at SFO,) and factor down from there.
For information on getting to Antigua Capilla B&B in San Miguel de Allende from various airports look at our blogs labeled "Transportation."