It is current practice that booths are available for sale to Members whose dues are current. This is published in the prospectus for each meeting. This is controlled in REM as follows:
Exhibits>Exhibits>View [NAME]>Planning>Booth Spaces>Edit>Prices>Edit>Setup>Price Attributes>Is Organization Member>Yes

These steps must be completed for each booth level - however, once set up when booths are cloned from year to year this restriction is carried over.
The outcome of this control is such that only Members and Associate Members may purchase booths via the booth self-service portal.
