Q: Can I sell/transfer my User Key to someone else?
A: No. Cfr the User License Agreement MuLab & MUX User Keys are personal and not transferrable.
The reasons are these:
1) A MuLab & MUX User key is a personal key and may not be given to anyone else.
IF user keys would be transferrable, there should at least be an admin fee for creating a new personal user key and updating the database.
2) If the original user has got support on using MuLab / MUX, and the new user would also ask for support, then we're doing bad business for that's 2 times support for the price of one. And where would that end if that second hand user also transfers his user key, and so on and so on.
That would mean that, at least theoretically, selling 1 user key could lead to supporting many people, and would cost us much support for almost no income.
That would simply not be fair, not to MuTools and not to all users as they will implicitly suffer from that bad business. (e.g. slower development)
So in fact IF user keys would be transferrable, there should also at least be an renewed support fee. (in addition to the admin fee)
3) When the original user has used MuLab/MUX for some time, we think he has taken advantage/consumed a portion of all the R&D work MuTools has put in creating these products.
This R&D work takes time and money of course. IF user keys would be transferrable, this would decrease the return MuTools receives for all the work.
And so this should be compensated in some way, for example by raising the price. But we prefer to keep the price low and to use personal user keys.
4) Summing all the above reasons and related costs simply leads to the conclusion that it's totally fair to ask a new user to buy his own personal MuLab / MUX user key. Certainly taking the low prices into account!
MuLab XT, MuLab UL and MUX UL User Keys can be purchased in the 
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