I did the rounds of the Tokyo shops a couple of weeks ago. In general, the owners and employees are very friendly and helpful, even with limited English abilities (n'attendez pas qu'ils comprennent un mot de franšais!). As all of the shops -- whether in Tsukiji or on Kappabashi-dori -- also sharpen knives, all day long, for their commercial customers, they are very experienced. Have no fear that they will do a good job "opening" the knives for you. The person with whom you spoke was no doubt just protecting the shop for all eventualities -- "managing expectations".
Which shop is this? I found the staff at Union Commerce and Tsubaya (across the street from each other in Kappabashi) to be extremely friendly and helpful and both shops have someone on hand who speaks English. TDI, Kamata and Kamaasa were friendly as well, with a little less English. The blokes at the shops in Tsukiji were also helpful, in spite of the fact that they were incredibly busy on a Monday market morning.