A good sales manager can increase sales 20% -- but that comes from good management, not through selling that amount.
The problem is sales managers are often saddled with excess duties.
What the sales manager should be doing is hiring, training, and helping sales staff sell more products for more money. Period. That's a full-time job.
I also believe there's a conflict when someone's a part-time salesperson and a part-time manager. The selling sales manager ends up getting the best leads and doesn't have time to help salespeople. Until a full-time sales manager is obtained, that role is best filled by a company principal.
What should a sales manager do on a daily basis? Monitor the goals, attitude, and whereabouts of each salesperson and each potential job. Evaluate each salesperson's performance. Call all clients within 24 hours, introduce himself, and thank them for their business. Sound like a full-time job?