Your undergraduate GPA will definitely be a hurdle for a top-20 school, and is at the low end of the range to be sure for a top-10 school. They will pay particular attention to the business oriented courses so low-grades in those courses will raise questions. I do think your graduate GPA will help you to overcome the concern to a large degree, especially if you can point to improved performance in conceptual areas that you struggled with in college.
The positives of a sales background are that you can highlight your client-facing skills and persuasive abilities. The challenge for you when applying for an MBA is that most sales roles don't offer the chance (in the early years) to manage teams. Exposure in a sales role to strategic planning and financial analysis is also limited as a general rule. Therefore, the real test of whether your work experience is sufficient or not is whether or not you (and your references) can supply examples from your professional history that will convince schools that you have management and leadership potential and the strategic thinking and analytical aptitude that MBA programs value.
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