The decision did not name the agency business which the dispute was over and Cartwright refused to when asked today as well.
In the court case, Robins sought summary judgment after he entered into the deal with Cartwright in 2016.
It was agreed that the $750,000 would be paid in monthly instalments.
Cartwright paid the instalments up to $226,000, albeit intermittently, the decision said.
Payments were made up until mid-2018 "and [Cartwright] has since made no further payments", the ruling said.
A balance of $523,000 was outstanding under the arrangements but Cartwright offered no direct explanation to Robins about why he stopped making payments, the decision said.
So Robins sought the rest of the money via the statutory demand in court.
But Cartwright counterclaimed alleging breach of contract, seeking Robbins pay him damages. The amounts were to be quantified at the court trial.
The pair had agreed to operate the real estate business jointly, with Robin's involvement gradually decreasing.
But Cartwright argued in court via his counsel Costas Matsis that he was "induced" to enter into the agreement and that Robins had made misrepresentations.
His assertion was that because of pre-contractual misrepresentations made by Robins about the real estate business, it was only worth in the vicinity of about $30,000.
On that basis, Cartwright argued he had overpaid for the business by nearly $200,000.
Cartwright also complained Robbins moved out of the business premises soon after the sale deal was signed.
The only value of the business was the database "which ended up being predominantly filled with low-value cold call prospects worth no more than $30,000", Cartwright argued.
But Robins argued the matter was a straightforward case of the monthly instalment due under an agreement for sale and purchase of a business not being paid.
There was no dispute about the contractual terms, no dispute that the payments had not been made and Robins said he was therefore entitled to the judgment.
When asked to comment on the outcome of the case on Friday, Cartwright asked: "Why is that news? It's a business arrangement. Why would it have anything to do with anyone else? We're still in a legal situation here. The High Court decision is only one part of it."
Cartwright refused to name the business he had bought, would not say if a Court of Appeal case was planned and objected to being asked about the case. Attempts to reach Robins were unsuccessful.
The judge said a central plank of arguments made by counsel for Robins was that if Cartwright had the concerns he now claims to have - including believing the business was only worth $30,000 - he had not previously raised any of those issues with Robins.
"Accordingly, summary judgment is entered against the defendant in the sum of $430,650 together with interest payable under the agreement of $87,531.58," the judge said.