Tatiana, I've used a few services with varying results. Here are a few notes for you.
Designing your Sales Process These companies can't design your sales funnel for you - you'll need to do that before hand, as using them "experimentally" can be expensive. Be sure to spend the time up-front to develop and test your sales scripts, objection-handling approaches, and closing statements. The more finalized your material, the better your results.
Trial Session Most reputable sales or lead-gen providers will require a paid trial run, even if they are a commission-only system afterwards. Be prepared to provide them with a list of potential targets (or to pay for use of their list) and to have them test your scripts before giving you a quote.
Require Guarantees Maintaining the relationship with such a provider is time-intensive. You need to keep them informed as your product grows and improves, and that can be a huge time sink if they aren't generating results. Be sure to include a minimum number of leads/sales as part of the contract.
Lead Gen vs. Sales Force There's a large difference between these two services, and bargain-basement service providers often confuse them when pitching them. Lead Generation services will warm up a contact and pass it to you. They don't need to train people as much, so will often have commission-only arrangements. Typically you'd pay "per lead" or "per appointment". Outsourced Sales Forces will actually be a sales arm for you, but you'll need to help train and equip their sales force, and they'll often act as if they worked for you. I've found that this typically only works well for products that are more of an impulse purchase. Products that require a consultative sale haven't worked for us in this method.
Here are some companies I've had (or peers have had) good success with:
Another way to "outsource" your sales and marketing is to implement an affiliate program.
In the end of the day, you are simply paying a commission on a measurable event to take place (usually, a "sale") so why not implement an affiliate or referral program as well?
Think of your sales and marketing as a process that you have to walk your leads through and break them into several different step, each one bringing the lead closer and closer to doing business with you by removing their hesitations (fears) and increasing their trust for you.
Most folks forget to properly nurture their leads and are trying to make the sale on the first go even if you have a free trial that does not matter. So instead think about what the different steps that the leads have to go through and then think of which of those steps you can delegate (outsource to a person or automate to a machine) to a third party.
Step one -> The prospect comes to your website via search or ads or you have someone call them to offer a free report (telemarketing)
Step two -> Prospect converts into a lead in exchange for your free report and over a couple of days you send them really awesome information via email autoresponder
Step three -> At the end of the mailing process you can have your outsourced sales rep call the lead to schedule a meeting with you to audit their needs
Step four -> during the this stage you audit their needs and if and only if there is a fit with the value that you provide then you find out the following; who is the decision maker at their firm (if not speaking to decision maker stop and ask for him/her so that you can start the audit from beginning), budget, and timeline.
There you have it, so think properly which parts of your sales process you want to automate and which you want to outsource. Remember to also provide value upfront so the prospect sees your marketing process like cheese and not like a cat (note I am comparing your prospect to a mouse in this analogy - not in a bad way though).
If you have more questions and need one on one consultation on outsourcing your marketing and sales give me a buzz.