Hotels and online travel booking companies tend to have a marriage of convenience — one that savvy travelers can exploit. When hotels are having trouble filling rooms, they will grudgingly pay Expedia and other online travel agencies commissions of 15 to 30 percent to help reduce the vacancies. But when the beds are filling up, the hotels would much rather avoid those hefty commissions by having travelers book directly through the hotel’s website, call center or authorized brick-and-mortar travel agent. Which is why lately, with average occupancy rates in the United States at the highest level in a least a generation, hotels are dangling inducements to get you to book direct. The tensions between hotels and online agencies are nothing new. But the continued rise in occupancy levels is making hotels feel they have increasing leverage.