The number 1 rule for long-term individual investors picking funds used to be simple: look for low fees, also known as low expense ratios. Investors do get rewards from low fees; but they should also watch out for higher, hidden fees in the same funds, as well as strategies that lure investors into higher-priced products or into paying more for advice. Instead of asking about low fees alone, ask what you are paying over 10 years, including all fees. "What is the cost, all in, for 10 years?" said Eric Johnson, Director of the Center for Decision Sciences. Investors should also watch out for marketing strategies that get you in the door on a low-fee fund and later sell you into high-fee products and services. "There's a sense in which index funds or target-date funds have become the standard," said Johnson. "They are like milk and bread in the grocery store. It means the firms are making money other places."