Abstract: A system for assisting in selling vehicles includes a database server (107), an application server (103) to access and handle information stored in the database server, and mobile terminals (101) each connected with the application server by communication channels (115, 113). Each mobile terminal includes a budget module (306), a link-switching module (303), a data synchronization module (309), a data filter module (307), and a data storage (310). The link-switching module is for switching states of connection as between the mobile terminal and the application server. The budget module is for calculating fees relating to vehicles using budget definition information stored in the data storage. The data synchronization module is for downloading information for synchronization from the application server. The data filter module is for filtering modification of data in the data storage, said modification performed when the mobile terminal is disconnected.