Final answer:
Complimentary upgrades in the hotel industry are based on availability at check-in time and can differ for elite members. They may also be provided for a portion of the stay. Hotels can also upsell premium category rooms to elite members.
Step-by-step explanation:
Complimentary upgrades in the hotel industry are provided based on availability at check-in time for both members and non-members. However, for elite members, the availability extends to the entire stay rather than just at check-in. Additionally, elite members can sometimes receive upgrades even if the availability is not for the entire stay, allowing them to enjoy an upgraded room for a portion of their stay. Furthermore, hotels may also choose to upsell premium category rooms to elite members.