The first piece of advice was here. Here's the second one:
#2: Sell at every step
Until the money is in the bank, every interaction with the client is a sales interaction. When dealing with businesses, even a signed contract won't protect you from pissing off a customer. At the end of the day, if you're a startup and you piss off a company 10x your size and they demand to terminate the contract, what are you going to do? Nothing. You'll agree and let the contract slip.
With that in mind, it's important to make sure that every interaction before the money is in the bank reinforces your sales message. One classic mistake is sending a horrible looking contract. The contract is a sales document, and if your contract looks like shit, you look like shit. It imputes the value of your service or product just as much as Apple's packaging does for the goodies inside. Even your invoices should look good.
Another mistake is sending bad-looking status reports or plans of the ongoing work. Even the report that outlines how the project is slipping should look good and convey your sales message.
In this day and age, it doesn't take much to produce gorgeous-looking sales materials, so if you fail to do that, you fail at something very basic, and will rightly be penalised for it by losing sales.
So, think through every client interaction in the sales process that you mapped, and make sure every point of contact, be it a contract, email, meeting or phone call, projects the image you want to impute to your business.
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