For me, it's sh*t like 'could of done this' or 'should of done that' - how dim are you if you don't know it's 'could have' or 'should have', HAVE for fox sake.
While I'm on it, for those who do not know, it is 'too' in the context of 'too' far or 'too much' - not 'to far' or 'to much' - 'to' is used in the context of 'to be or not to be', or 'I'm going to have an effin rant if the dimbos do not try harder.
Last one, count this as a Christmas present if you are one who missed out on a reasonable education under the Labour government - 'their' is used when something belongs ( or sort of belongs ) to someone ie 'their team' or 'their stupidity - 'there', quite simply implies 'over' there, it generally implies a place eg 'I was there'.
'They're' is short for 'they are' eg 'they're wankers', 'they're stupid' ( could be people who think Wellens is good ) etc. It is always, and only 'they're' if you could use 'they are', end of! Merry Christmas.