A large number of online stores tend to ask customers to sign up or register to their store during the checkout process. Whilst this may seem like an appropriate time to ask people to register with you, not everyone will want to and it can prove to be quite an annoyance if you are in a rush.
Asking for someone to sign up for an account during the checkout process is a bit like asking someone for a second date just as you’re coming close to agreeing on a first date. People do not want to commit that far ahead and it can come across in the wrong way.
Most online users want to buy there and then and you should make it as quick and simple for them to do so. Although forcing a customer into a full-blown sign up is far from preferable, you can still offer that as an option during the checkout process. People like having the option but they react negatively into doing things they do not wish to proceed with.
To build a relationship with your customers you will need to gather certain details about them. Whilst having them complete a full sign up form could gain you this information right there and then, it could also lose you a sale if you force them into it. You will gain their name and email when they checkout anyway, this is a good start but try and be creative with other methods of gaining information from your customers
If you really want people to register and sign up for an account then offer this to those customers once they have bought from you. Not only is this likely to come across as more professional and welcoming, but since you have done business with them already your customers will be far more receptive to your suggestions and further offerings.