For each of the games, there are deal, rule, and scoring preferences that must be same for both players.  These are defined separately from your normal (offline play) preferences, and supercede your normal preferences when you go online.  Agreement between players is more likely to be successful if few, if any, are specified.   This example is from Rummy 500:

If the online preferences are different, the guest is presented with a list of differences before deciding to connect.  The guest may decline the connection, counter with their own online preferences (which may be temporarily adjusted for this session), or accept the host's preferences.

If the guest counters, the host is notified of the terms as part of the acceptance notification.  The host may accept or decline.