I strongly consider management to reconsider this decision so that I may continue shopping in your outstanding stores. Until such time, I can personally guarantee you the loss of my money and that of my friends and family.
The first part of this sentence doesn't make sense.
I'm not sure what you're going for there. "I strongly suggest", maybe?
If that's the case, it should be something like, "I strongly suggest that management reconsider this decision."
Also, the "personal guarantee" of loss of money from family and friends is not something I'd include.
The last part, I know for a fact that companys consider MASS quantities of these types of letters but a single letter by itself means nothing. They don't really believe that most people will really never shop there again and they certainly don't believe that most of your friends and family won't either. They'd be right too. Most people who make these "promises" will be back in a few weeks/months. I'd leave that part out entirely, it's only for dramatic effect and rather hurts the credibility more than enhancing it.
Still happily answering to the call-sign Peetza.
You do not HAVE a soul. You ARE a soul. You HAVE a body.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.