If you can file the rebate online and mail the documents later do so. You will get the rebate faster. Always make photocopies of what you send in the mail.
The companies know they will lose business if you do not get your rebate.
Correct - This is why I generally trust rebates from reputable companies.
A reputable company is not gong to risk their reputation by trying failing to properly honor rebates.
If you see a rebate from a flybynight company that does not have a reputation to protect, be wary.