If you pay taxes in México, you can save the ISR and IVA Mexican Taxes, if you can prove to SHCP (Mexican equivalent to IRS department) that you already do all as possible to collect.

You should not pay a tax for an income that you don't receive. And the law protect you.
Article 31 paragraph XVII of the Mexican Law of Income Tax, regulates the exceptions in the payment of such tax, and include cases in which, for lack of payment, this obligation may be deductible.

This legal text does not say anywhere about a 'certificate summary of uncollectible account' that's need to be relesead by any company or institution, however for a better transparency in its taxes declarations, many accounting firms ask their customers to exhaust all means to retrieve a case, and in such cases DEBT COLLECTION SERVICES MEXICO can help by issuing a formal document that endorses all activities that you, through us, tried to get your money back.

Definitely there will always be a bad credit risk, but at least make sure not to pay a tax for an income that you did not obtain.