Your policy of refusing to support secondary sales is very disappointing. I am currently transitioning from 3ds Max to Modo, and had a Thea Render license for GPU rendering (Max plugin). Since Thea has no plugin for Modo, I tentatively planned to go with Octane render (for Modo). Thea allows a user to sell/transfer the license, but the license cannot be resold after that. So, I was able to sell my license of Thea Render.
I have a friend who purchased the Octane Render bundle for Lightwave last year, but has since sold his seat of Lightwave. He wanted to focus on one application (Modo) and decided that he preferred VRay (for Modo). That effectively leaves him stuck with a $600 license of Octane he can no longer use. I asked him if he would be interested in selling me his (standalone) license, so he could get some of his investment back, and I could get a price break in the process. He said he couldn't, because of your policy. Seems very harsh, because I work for a 3D software company and we too allow secondary license sales/transfers.
It's just part of life. Sometimes, for various reasons, people are in a situation where they simply no longer plan to use a license they purchased, and perhaps they NEED to sell a license to pay some bills, and if they aren't using the software, it seems very callous for the software company to tell them...."No, you are stuck. Sorry pal." You may reply "but we get nothing out of it, so we aren't interested." That's not true at all. You stand to get new plugin revenue and future upgrade revenue out of that license. It is a dead license otherwise, and you'll never get another penny out of it.
This current policy is a dissuasive one when I deliberate as to whether I should make an investment in Octane or wait a while and see if another popular GPU renderer is ported to Modo. The compelling aspect to that render solution is that one license operates on all 3D applications they have plugin support for. So, I could use it with 3ds Max, Houdini, etc., without the need to purchase multiple plugins. It is also significantly less expensive than Octane. While Octane certainly has it's own merit, software purchases can eat persons budget quickly and that is why I personally try to wait for sales or sometimes buying a license 2nd hand...in order to mitigate the impact they have on our personal budgets.