Clowns can be agressive, its sad but its the truth :/ maroon clowns are known to be a bit on the agressive side and so are tomato clowns. True percs are more agressive then ocellaris clowns which are by far the least agressive.
This is my advice to you. If you want clowns dont spend 50 extra bucks just because it says "mated clown pair" on the glass. Waste of money IMO, so to the tank with the 10-15 dollar ocellaris clowns (remember, non agressive) and buy the largest one in the tank and the smallest one in the tank. Now be intelligent about this... If the smallest one is the size of a fly dont buy it, but you want one clown to be smaller then the other. This way they wont fight about who gets to be the female in the relationship and they should live happily ever after. The end