I have made a simple XP command block shop only requiring 2 command blcoks!

The first command block has this command(Remove Parentheses):
give @p[lm=(XP Amount)] (Item Your Selling)

The second command block has this command:
xp -(XP Amount)L @p[lm=(XP Amount)]

Pictures To Refrence:
http://tinypic.com/r/ibamqf/5
http://tinypic.com/r/1i26vr/5
http://tinypic.com/r/2nicyky/5
http://tinypic.com/r/15g74ft/5