Or better still make sure that your sales consultant has a technical background with the application.
At least then you are less likely to end up with the problem where the sales consultant has oversold what the application can do or what customisations are possible.
Many people in the Dexterity Development world know me for my work as a pioneer of Cross Dictionary Dexterity Development. The driving force behind the development of the techniques involved was over selling of customisations.
Recently, this video was released which shows the commercial pressures placed on the technical expert.
The Expert (Short Comedy Sketch) (Direct Link)