First of all you need to hire a mature sales force with commitments and therefore are naturally driven. You can also have a blend of young upstarts but who seem hungry to earn.
Sales is commission driven and should be as such. However, when you offer a retainer, you get many upstarts who want to joyride on this as they look for an office job. Be careful not to fall into that trap.
You can offer a retainer based on achievement of first 2 or 3 sales or on a scale based on performance i.e. let's say you offer 20k as retainer for the first 3 months but the sales person has to achieve their target, failure to which you reduce it to 15k or 10k depending on what you agree on.
You can also offer a higher retainer to people with a track record in sales but still based on achievement of set targets.
Mukiha's point is crucial, money is not the only motivator and there's has to be suppport in form of training and development.You can get good tips from sales managers in various fields.
Good luck
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