The up selling feature in AShop lets you present your customers with 1 or 2 products that are related to the ones in their cart, when they are checking out. For example: a customer buys a PC, when he clicks Checkout he would be presented with the option to buy an Antivirus software for his new computer. He can click Add to cart to buy this item too and then proceed to the checkout, or he can choose to skip the offer and go straight to the checkout.
To activate up selling open the page Configuration->Shop Parameters in your administration panel and select "1" or "2" in the configuration option "Up sell X items before check out".
The next step is to relate your product to one another. This is done by first clicking the up arrow in the upper right corner of one of your product listings on the page Edit Catalog in your administration panel:
This will select the product and let you choose another product which is related to this one. Click the green accept icon in the upper right corner of the product you wish to select or the red cancel icon to get out of the relate products mode.
Now you will see a page where you need to confirm if the selected product should be related to the one you clicked the up sell arrow icon on. You will also be able to select a priority for the relation. A higher priority means the product should be more likely to show up as an up sell for the one it is related to.
Once you have selected at least one product as related to the first one it will be presented to your customers before check out, or after check out if you are using a payment method that collects the payment information from your customers on your own site (this is known as "1 click up selling"). If more than one product is related to the one the customer is buying, the up sell will be randomly selected in order of priority. For example: if your customer is buying Product 1 and there are 4 related products of which one has priority 9 and the other three all have priority 0, then the one with priority 9 will be shown first of all. If you want to up sell 2 items the second item will be randomly selected from the three with priority 0.