Definition: Given a travel related situation, and given a specific question about the situation, summarize the question into a title
Input: (In a similar vein to this question on hotel room upgrades and this question on flight upgrades...)

Most regular car rentals agencies have various categories of car - Budget/Economy, Compact, Midsize, Fullsize, etc. The names vary from agency to agency and around the world, but the principles are similar.

Generally the "better" the category, the better the car - larger, more luxury, etc.

What tips or tricks can you apply to get a better car or better benefits than you originally booked? This might result in a "better" car, or perhaps something else such as a free satnav included, free miles included, or some other perk that improves the overall value for money equation.

Some of the tips I've noticed are:

Being a regular renter with that agency, e.g. status with Hertz Gold Plus Rewards.
Turning up to a smaller (often in-town) rental location when they only have a few cars left, which can bag you a free upgrade (although this can also backfire and you can get a dismal car!).

Output:
What tips or tricks can you use to get an upgraded/better hire car?