Special feature requests were tied to minimum spend contracts.
A somewhat smarter pricing model, in my own opinion, is rather than charging someone $200 for a phone call, sell them "coupons" in advance where one coupon equals one support contact. When they have used up N percent of their available coupons, send them an automated e-mail and tell them that future contacts will be denied unless coupons are available.
This way, you get the money up front, which is good. Customers that don't contact you a lot are also happy, because they won't need to "re-fill" for a long time -- and annoying customers that call you just to check if you got an e-mail will burn through their coupons in no time.
This way, there is no explicit cost for a single phone call that can be challenged by the customer, it's simply an objective way of charging "support contacts", and it's up to the customer to minimize those contacts if they want to save money.
What constitutes a contact is up to you, but in my mind it would make sense to classify "ticket creation" (not replies) or "phone call" both as separate contacts. This also makes tickets "worth" way more than a phone call, so you incentivize people to stop calling unless absolutely necessary.
I have never worked with a company that bought Oracle products, but I still have a bad experience from their presale calls.
If you say you're not going to answer in a positive, then you also shouldn't answer in the negative.
So replying once in the negative reveals negligable information and probably does not risk identifying the vendor at all.
Of-course, I did have one call that took me only 5 minutes to drive to the site and the three minutes to change the toner in the printer.
The executive secretary who would not talk to me over the phone because she was so important suddenly found she would have to explain a two hour service call (1 hour travel, 1 minimum service time) to her boss. :)
Very few rich customers aren't a handful. Let them make you rich first, then if you're lucky, you'd be surprised how quickly you outgrow them and have all sorts of tools at your disposal to deal with them.
If they’re not and I call you on the phone for 1 minute and you send me a $200 invoice, I’m not paying it. Sue me and see if the invoice is a contract.
An invoice is just a formal request for payment. It doesn’t itself legitimise that request.
Otherwise I could send you an invoice for $1m out of the blue and according to that logic you’d have to pay me.
There must have been some agreement, most likely in the form of a contract, in advance, for you to have to pay that invoice.
And even then, some companies employ large teams of people whose entire job is trying to avoid or delaying paying invoices in order to improve their cash flow.
An agreement with consideration is a contract. (Consideration means something of value is exchanged.)
However the agreement is made. It could be on the phone, text, smoke signals, anything. Though if it's denied later you may have a hard time proving the contract was made.
Usually an invoice is sent after an agreement. You have to pay those because you already made a contract to pay (written or not, formal or informal), and quite often an invoice provides formality that was lacking before, crystallising the expected amount. The act of paying it generally signifies final agreement to that amount.
For business contracts, often an invoice is the first time the buyer sees the exact amount the seller is expecting, because of details that weren't hashed out in advance (no need). For example per-hour freelancing can be like that; the buyer learns the number of hours the seller claims to have worked from the invoice.
But people dispute invoices all the time if they aren't expected or differ significantly from the amount expected.
Be polite instead.