But now I think the best solution would be a limited amount of items that one avatar could rent at a time.
Why not 2 or 3 items at a time..
But more probably this amount should not be more that 1 rented (or lended, since it would be impossible to differenciate) item at a time. (exception for armor/plates, for sure 7)
That would solve nothing, sorry.
Look at FEN token trader what weapons have been offered.
Its different weapons for different levels, now the renting mafia would simply buy all of them and renting them out.
How it is now, sure the biggest wallets bought this weapons and try to sell it now for a profit, because they just need one of them (the best one), the others are available in trades.
If some renting mafia, would have bought all, it would be available for rent, but that also means for MU for those using it.
It would become completely useless to invest to buy better gear, as there would be no gear for sale available, just for renting!
Limiting item numbers for rent to less than 7 would make it impossible to rent out full armor sets.
Limiting item numbers for rent to less than 14 would make it impossible to rent full set plated armors.
So limiting items, solves nothing.
And you already pointed out the next problem, if number of items for rent will be limited they simply would use multi accounts, what not necessary would breaking the EULA as most people have relatives that actually dont play EU. Simply ask them to create an account, giving real personal data and banking informations to MA, and all would be fine within the rules ToU/EULA.
If my brother (who actually dont have an EU account), would withdraw some k PED every month, if he makes an rental account, and give it to me in RL, what should MA do against that ?
MA could do nothing, and it would be really bad for the availability of items for trade in EU, they would be gone in no time.
It would also skyrock some MUs on efficent items, as you could simply make back the money by charging higher rents.
Example: A weapon that cost now 50k PED, could be bought by rental Mafia at lets say 100k PED, and then rent out for 50 PED/ day. ROI 5.5 years, not a bad investment! That would be better than AUDs/CLDs/MDs, but double the MU of that specific item, and this item would be off the market from that moment and everybody would like to use it had to pay the rent, so no advantage from beeing unlimited, you still would have to pay MU in form of rental fee.
So please NO, dont introduce this!