I am up to date on discussing any language or operating system need that an employer describes to me as being critical to accomplishing the job. As a recruiter for 25 years, it was not necessary that I do the job that I recruited for. That would be like requiring employees to be dead to work for an undertaker (NO I DIDN'T SAY THAT, but wanted to).
Remain completely silent and let the irate client vent. Assure them you will check the status of the problem, follow-though with the action you promised (apology) for any enconvenists, build trust and show the customer you understand his or her problem. (by saying the word important its helps break the venting cycle
This was one of the more difficult questions asked, for I do not have a lot of experience in sales jobs. However, having helped my family build and create a business from the start, marketing and sales tactics were necessary in gaining loyal clientele in order to operate the business. With that being said, I was not unfamiliar with the idea of collaborative selling, and was able to explain various situations when collaboration was necessary in order to maintain business in the long term.