Next time you get someone to look after your fish I find its always best to write out detailed instructions, then go through it with the person. Most importantly show them a week before how to take care of your fish and then for that week get them to do everything with your supervision. That way you can pick up any mistakes they are making and correct it before you go. It sounds like your fish sitter was overfeeding by quite a large amount. Make sure the fish sitter has a good understanding of the fishes needs aswell, and write down things for the person to keep an eye out for. such as excess food, cloudy water, algea blooms, water level too low etc. There is no reason why you cant have a years vacation if your sitter is trained properly.