Just learned something wild about car rentals that could've cost someone over $1,700 extra. So this person booked a Hertz rental for Hawaii in early April at like $570 for 10 days. Then her flight got delayed by a few hours, so she extended the reservation. Price went up to $640, whatever. But when she checked again a few weeks later? It jumped to over $2,300. No explanation, no warning. Turns out do car rental prices fluctuate this much because most companies have this sneaky clause - if you change ANYTHING on your booking, they recalculate based on current availability and rates. Even tiny changes like adding a car seat or shifting your return time can trigger it. The company eventually honored her $640 rate, but honestly she should've just grabbed a rideshare instead since she barely used the car anyway. The whole thing got me thinking about how rental car supply is still crazy tight, so prices are all over the place. If you're booking a rental, here's what actually matters: don't book through third-party sites if you can help it, book extra hours upfront instead of extending later, and seriously - check your reservation multiple times before your trip. Don't wait till you're at the counter to discover some nightmare charge. Better yet, if your plans might change, just book the rideshare from the start. Way simpler than gambling on whether do car rental prices fluctuate in your favor or destroy your vacation budget. Has anyone else gotten hit with surprise rental car fees?