There would have to be very strict safeguards but I think euthanasia could work and could be made safe from exploitation.
The procedure I would want to see would be something like ;
Terminally ill patient approaches their hospital consultant, who must agree to the request
A second consultant must also agree
A process then takes place where the police are informed, this is to ensure that the person in question has not previously been a victim of crime by anyone likely to benefit in that person's will. A full will must be supplied to the police and criminal records checks made on every major benefactor.
Reports from all of the above people can then be considered by a High Court Judge.
Importantly, no case should ever be allowed to set any president. Every case must be a unique ruling.