One of the things i hate from PS is that you can see or calculate the stock a shop has. Adding random quantities till you get the "there is no more stock" or adding with "+" you will know the exactly stock of certain key products. Rastering these key products through days you will know if your competitor is selling or not . And of course using any similar method your competitors will know your sales. This info is so valuable that I dont know how PrestaShop hasn´t done something to avoid that.
I want feature for hiding that info. Now, as i sell rubiks cubes, i want to allow to order 4 or 5 maximum of each product, as it is very difficult that a customer wants more than that quantity for one cube, and this way competitors will not know if i have 5 or 200 units of the same product. If a customer wants more units it will appear something similar to "For those quantities contact the administration.".
Indeed, problem you described is definitely the one of the most important thing in prestashop to improve in the future releases of the PrestaShop engine. Anyway, at the moment you can use module to define maximum quantity of product that customer will be able to order. This module allows to define that kind of limitations you mentioned. The most important thing is fact that you can define different quantities for customer groups. So, if you already have trusted customers - you can grant them possibility to order more quantities of products. Anonymous guests of the shop (so also your competitors) will not be able to check quantity of the product, because you can create limit for anonymous group of customers. When they will try to order more stuff, they will see information that you can define by yourself. In simple words: with this addon you can STOP YOUR COMPETITORS SPYING YOUR STOCK