Sales probably are different for every shop that sells pin backs. My shop has had about 30 sales in 4 months. Rate of sales has slowly increased since opening.
Your sales will depend on a number of factors - How easy it is for shoppers to find your shop, where those shoppers come from, and whether or not you're selling a product shoppers want to buy.
Here are two links that will help you find customers; well, if do the stuff in these articles shoppers will be more likely to find your shop:
https://www.etsy.com/help/article/34234144469https://www.etsy.com/help/article/247?ref=help_search_resultDo what is suggested in those articles and you'll be off to a good start. Read the entire Seller Handbook, too.
The two most important rules are, in my opinion:
1. Practice Patience.
2. Realize and understand there are no guarantees of success.
Rule number 1., good customer service, and doing what is in those two articles will go a long way towards reaching it.