If you are thinking of growing a sales team then you might be consider the option of using an outside agency. There are both pros and cons with this that are similar to any outsourcing you might try and do.
Your Own Person
Hiring internally means someone can learn about your business, they are going to be with you on a day to day basis, they will meet the people carrying out the work etc This should give them a much greater investment into your business. Having someone there day to day also makes it a lot easier for you to keep an eye out for them. (within reason)
The main benefit with an agency tends to be you are getting a team of highly experienced people that you probably couldn’t afford normally. You are getting much less of their time then if you were to hire someone obviously but they may be better organised to get more from that. The major disadvantage is of course that they are a third party, and despite all the spreadsheets in the world you have no real control over them, and obviously not all agencies are created equal. The major disadvantage with any agency is of course that a big part of sales is building relationships and you don’t want your customer doing that with someone who ultimately isn’t associated with your company.
There is often a lot of hard leg work involved in Sales, depending on your industry it might be worthwhile to hire a call centre to try and tee up opportunities for your internal sales person. This combination makes life easier for your sales person and can be especially effective where an internal salesperson might need a level of technical or product knowledge.
I think targeted campaigns or new markets might be an area where an agency have the upper hand. They can look at your offering afresh, and the success of their campaign will be easier to judge as it will be in a new market. This also means you’re not taking time and resource away from your internal sales team who need to concentrate on those areas you know will make you money.
Gun to My Head
If I was forced to choose I would suggest that an Agency would generally be better in the short term, but if you’re looking for long term sustainable sales returns then you most probably need your own staff/team. Obviously sales as an industry is notorious for its high turnover of staff, but if you take your time in hiring the right person and treat them right it will be worth it.