You shouldn't offer or auction off a single card without first going through the entire set. Some sets are only accessible through that require a single player, but others are also possible to earn with a little luck throughout the year.
This is a fantastic way to earn the exact cards which people who sell their cars, but without breaking the bank. You can add additional players to any set with some patience. Even if the reward isn't an upgrade, the reward will always be worth more than the total of elements that make up the card.
The idea of avoiding the stores is a good idea as card offerings improve with each season. Spending money in the stores today for cards will soon go to waste when the cards of tomorrow are in stock.
However, the cards that are limited-time which represent the greatest waste. They're appealing because contests only offer enough of one set of cards to create a stunning card. However, this wonderful card may not be as good after the next limited-time challenge hits.
The game is able to automatically rate cards based on a number of factors, all the way up to 99. However, those who study stats will notice rank 78 cards are more sought-after than rank 99 cards. It is vital to verify each card's individual performance.