Buying and selling transactions using internet media has advantages related to time and costs. However, buyers often feel difficult when accessing online websites. There are several types of errors that are experienced by buyers when using online buying and selling site services. It is including mistakes in selecting display menus, difficulties in finding items needed because there are too many choices available, errors in interpreting menus used, and sometimes difficulties in knowing product specifications because no relevant information is available on the site. In this study, we discuss the application of the HTA and SHERPA method to assess one of the online buying and selling sites currently used by Indonesian people, namely B.com. There are 100 respondents participated in this study. The study methods are including error identification, analyzing the error using SHERPA, and evaluating the website design. The result of the study provides some recommendation to the online buyer such as ensuring the quality of internet network, filling the data carefully, and confirming the purpose and nominal value of the transaction before it sent to the seller.