The problem with Verizon honoring salespeople's offers is that Salespeople will offer practically ANYTHING to get new customers to sign up. Having worked tech support for various companies, I can tell you that nothing sucks more than getting a call from a customer asking about a promise a salesman made that simply isn't possible.
There needs to be more accountability for salespeople, but the fact of the matter is that there isn't. They promise the moon to get you to sign up so they get their commission, but never have to deal with the fallout. Tech Support and Billing get blamed for the lies that Sales tells.
Until companies (not just Verizon) stop looking at Sales as "revenue generating" (and therefore beyond fault) Tech Support as an "expense" (and therefore just a problem) nothing will get better.