The development team must be consulted on these decisions or you will never get out of that cycle. If you aren't managing the team, then one of your line managers needs to advocate for the development team. If they are part of the problem, then you may want to consider other employment options.
Generally speaking, Sales shouldn't be committing to anything without the Product Management's acceptance, who should obviously be consulting with the development team for timelines. There's really no good excuse for bypassing this in a big or small company because ultimately the Sales team will take some heat for under-delivering (whether in quality or scope).