[Pottus]

You need to use use sscanf() or strval() to get the sID.

ex.
if(sscanf(params, "i", sID)) return SendClientMessage(playerid, 0xFF0000AA, "Usage: /strval <skinid>");
or
sID = strval(params);

Using sscanf() is probably the better way since it takes care of checking if a value was actually given.