Remember, your customer success people are not by nature sales types, they are nurturing-support types. Let it be known that you have such a specifically dedicated group to do only that as you sell and get acceptance as part of the value your sales team brings to the prospect/customer. When to bring them in?
In fact, as part of the selling process, it's good and frankly quite powerful as a sales tool to allow a prospect to talk with a customer support person to learn from them what they do.
For sure, Formally bring them in at the close, intro them to the customer and let them work out contacts, implementation processes, schedules, who to do that with, manage the rollout, best times to talk, even a regularly scheduled call where any questions or emerging issues can be discussed and the process put in place to resolve them.
The customer success person should be known to a prospect and a new customer or existing customer asap, and of course already be valued, known before the sale is made since that kind of support is part of the sale and a differentiator re getting the sale.
Upon closing, the sales person should then, with the customer knowing this is happening, move the customer over to a specific person in customer success and in fact make the introduction so to speak. Next, when that is done, the customer success person should call the new account and with them, clearly define contacts at the new customer, who they are, how to reach each other as an account profile.
Doing things this way we Now we have a support relationship inplace. The support person should know how to ask about changes at the customer that could reveal new opportunities, need a friendly sales visit. keep the customer.
When not to use a customer support person re the sales cycle:
PLEASE Don't ever ask customer support to sell or actually do any upselling because it goes against their grain of who they are, they see it as undermining their credibility as a support person to their accounts and their core traits won't let them do that. It won't work. Clients don't expect selling or upselling from the support arm and resent it.
Dont put them in the sales seat while you are selling and make sure they can softly defer sales related questions to the sales person as "better equipped to answer xxx question" and then take the steps to get sales directly and immediately involved.
How and when sales can help a customer support person seamlessly become the contact/account manager person:
Spell out clearly for your customer success folks when a sales person should be referred and or the customer/prospect told that the "expert'" in the area under discussion is the sales person.
Result re cementing the sale and keeping the client:
When that sale is closed, the Customer support person is now a "partner" to the new customer, is seen that way and stays that way so the relationship is strong, cemented and can actually grow opportunities at the account.