I have been using PayPal since 2004. And i buy a LOT and also sell from time to time using PayPal.
Unless the online web site of the developer have a system to buy that redirect you to PayPal, like ZHL Model has, normally the seller has to send a "PayPal bill". The seller send the bill to the "PayPal email address of the buyer". Shipping and any other cost is included. The buyer open the bill link that will take the buyer to PayPal.... and pays.
Sorry I am writing all this. I am sure you know well the system. But I read there could be potential buyers that are not used to it .
I have never received a "link to PayPal" as you mentioned. Unless is something I am not used to see in USA. I always received a PayPal bill. To buy or to pay for services.
Another tip. This is a public forum and posting a link I am not sure how secure it will be. I will be afraid to pay opening a link.
My 2 cents. I almost do 90% of all my online buys using PayPal.
PS: Also be aware that sometime only certified members (I think that is the way PayPal call them) can buy. Depends on the setup, I belive from the seller side. Those members have a bank account linked to PayPal and are certified (if that is the term). Many sellers will not sell unless you are one of those members. That is for the seller protection. Also for the buyer too.
PS 2 : I have also paid many time just using the PayPal email of the seller.
You get a bill and the seller PayPal email. You go to your account and do a payment (send money) to the seller email that is registered in PayPal. Seller pays a fee fir this. Not buyer. And buyer gets PayPal protection.