Tried it in firefox and chrome and comes up as an error for me.

Also for me - with Edge

It still all hinges on whether they've visited the forum though, doesn't it?

What if you want to find someone who hasn't been to the forums?

That link + username is independent of the forum.

I have a list of sellers I found interesting, but not enough to save them as favourite sellers, and I have the links in a file, all in that format (with only a couple with str instead of usr). Most of them probably never visited the forum. It is just how the urls of eBay profiles usually are.

When you click on that link it goes immediately into an error. However, if you type it out exactly as the link and then put the persons username into it then it works. It is a pity the link won't hold and you have to type the whole thing out. So what I have done is put one username in as a saved link and if I want to search for someone else I just change the username at the end. That works, thanks.

The link works for me. I have just checked again. 

If it does not work for you though and you don't want to have to type it out every time, something I also do is go to my feed, saved sellers, then just click on a saved seller and when the page opens I change the username (the last part of the url)...