In some tournaments there are restrictions on the amount of stars you can have in your deck, and some cards can be used on lower levels, so they get put up for the lower levels at higher prices because some people will buy them. like wanda. level one she has 8 power, 1 damage. level 2 she has 8 power 2 damage. she only gets one damage, so you might as well use her on level one.
the most effective ways to gain clintz are: buy at least one pack so you can sell on the market (buying a pack with tourney gains doesn't count), and enter tournaments, like elo (gives out credits) and daily tourneys, or survivor if you want.