A 1-yuan link is a simple, yet ingenious way for a seller to sell any item they want taobao without any maintenance, storekeeping or having to fear being taken down or getting their account shut down.
The advantage for you as a customer is that they can buy anything from Taobao, which usually has the lowest service fees, both for the agent and platform fees.
The way it works is simple. The seller lists a product that costs 1 yuan. You buy this item x amount of times, so for a 99 yuan item you open the 1-yuan listing through your agents website, and then change the quantity to 99.
In the remarks field you say what item you actually want. In most cases you're also going to want to talk to the seller to tell them about your plan, then you have to leave your WeChat in the remarks too.
Some seller think taobao is catching up, so they are making 10-yuan links now. It's the same thing.