Banks change cash but casas de cambio (currency-exchange offices) are usually quicker and may offer better rates. ATMs widely available. Credit cards accepted in many hostels and most midrange and above hotels and restaurants.
A 10% tip is expected in restaurants (often automatically added to your bill in tourist towns such as Antigua). In small comedores (basic, cheap eateries) tipping is optional, but follow local practice and leave some spare change.
Homestays Better to buy a gift than give cash.
Hotels Q10 per bag.
Restaurants 10% maximum (if not already included).
Taxis Not customary.
Trekking & tour guides Q50 per person per day (extremely optional).