A single-source approach requires a lengthy justification as to why they are the single option. Manipulation of the specifications so that you believe there is only one option does not require this justification because it's not explicit. In fact, it's possible that you are mistaken and another vendor could win the open (not single-source) contract.
Well, yes and no. Yes, when a single-source strategy is adopted, the spec is written for that supplier, but that does not mean that all cases where the spec is written with a specific supplier in mind are single-source bids. Sometimes it's an end-user trying to manipulate a bid so that only one supplier can answer. That's the distinction I'm trying to make.
...this isn't accurate. Intentionally writing a specification that only one party can meet is in fact called single-sourcing.