No no no! The whole point is to use the vinegar to achieve a more optimum salt distribution. If you salt after, you only get salt on your top chips (and too much at that). Judicious use of the vinegar as a distributive agent, post salt-application, carries at least some of the salt to the lower layers, where it will bring more long-lasting satisfaction. Be grateful that the chip shop attendant is better informed than you appear to be; you are the beneficiary of his, doubtless highly-trained, expertise .