Rental car companies use a variety of labels to indicate the size of their cars. Each company uses different car brands and types, so you need to ensure you know what type of car you are obtaining.A compact car at one agency might be midsize at another.Many rental companies also offer customer loyalty or membership cards that provide free upgrades to members.ach company uses different car brands and types, so you need to ensure you know what type of car you are obtaining. A compact car at one agency might be midsize at another. Many rental companies also offer customer loyalty or membership cards that provide free upgrades to members.