Oh, that's silly. I deal with thousands of contracts per year in business and at home. Most work out fine. Issues and even disputes arise from time to time but those are generally resolved very quickly.
Yes, there may be more shady characters out there than you or I would like. But most of the time, contracts, even verbal ones, work and are enforcable.
Interestingly, in this case, Home Depot appear to have diverged from their own written policies and (in my experience) their customary behavior. Perhaps the OP did not tell the whole/true story but it's just as likely that a poorly trained, minimal wage employee screwed up. In the latter case, it is clearly Home Depot's responsibility.
Of course, all bets are off if this purchase was a special sale item sold on a receipt clearly endorsed with something to the effect of "no returns".
If the OP has fairly represented the details of this transaction, he will most likely prevail in, say, small claims court. A courteous conversation with the local store manager may resolve the issue even faster.
One thing I would do in his situation is to ask for a written copy of the store's returns policy -- there is a rather poorly written one on
If the OP has misrepresented the facts, there's little point in all of us pontificating on what might have happened.