No problem if wording is provided/they don't explicitly lie over the phone (twice?). Totally speculating (I guess this whole thread is, based on the word of one person) but I expect that the reason companies don't say "might be slow over Christmas lol" is to stay competitive around a period where buying decisions are make/break around absolute timescale certainty. I wouldn't get away with that with the service I run, I don't see why this is any different. If you want to promise something you should be prepared to a) increase resource to meet the demand/your predictable workforce issues, b) be honest with customers or c) be ready for complaints if you don't do a and b.
