I have bought handcuffs from many sellers over the years and some are very helpful and some not. I tend to get quicker responses on ebay than anywhere but they tend to not know much about their products, so are not all that helpful with specific questions.
I am not going to name names, but there are two dedicated companies that sell handcuffs that I primarily use. One is in the UK and one is in Europe. The one in Europe has a very varied selection and tend to be very very helpful with answering questions, although sometimes it takes some time before you get the response. The one in the UK is quite short with people, sometimes doesn't feel like responding at all but has great pricing.
I wish all sellers of handcuffs would be as eager to help answer questions and lead people to the right product. Several times I have not made a purchase from the UK site because of getting NO response to a question I asked or getting an answer that amounts to "no idea" with no attempt to get the information or check.
We are going to sites to purchase the right products we want. A bit of effort on the sellers part can go a long way to securing our business and coming back for more. As annoying as it is buying internationally because of shipping times, I have many times ordered from them just because they are nicer people.