The law puts the burden on the debtor to prove the debt was disputed, There are things the creditor can do to show the absence of a dispute. Look to see if they ever lodged a complaint about goods or services or whether they made a warranty claim. If they had no contact with the payee before sending the check, it is tough for the creditor to say they are settling a claim the creditor did not know about. It is worth putting in a requirement that all complaints be submitted in writing in the initial contract. There is a greater propensity for dispute because there is more gray area regarding the value of services.
Any professional service is more intangible than a product.
Conspicuous is one of the terms lawsuits are made of. If the language appears in the memo section of the check, it is most likely going to be considered conspicuous under the law. You might make an argument if the language appears in an accompanying cover letter, and not on the check. If the creditor is aware there is an issue when he or she cashes the check, then by definition, the notice is conspicuous. For instance, the check is often more than the creditor will get if he refers it to a collection agency or begins legal proceedings.