there is more than one group for transferring Private Sims, but "For Sale by Owner" is a good place to start cause i am one of the owners!
Since LL lowered the price of a Private full prim sim to $600 USD (which includes the first month's tier), group activity for re-sale of used sims has slowed somewhat, as the Sellelr will pay a $100 transfer fee (which the buyer usually reimburses) plus the buyer will pay $295 tier when it becomes due (moving and renaming the sim is included in the $100 transfer fee), so the buyer's total expense may be as high as $395 for the sim (including one month tier) PLUS any profit the Seller tacks onto that amount. So you can see how this figure is approaching the $600 LL charge for a new sim. Since the buyer usually receives the re-sold sim before the first tier is due, her/his cost is usually less than the $395 mentioned above. I'd estimate someone can save $100-$200 buying a used sim, depending on tier dates and Seller profit, if any.
Transfers of grandfathered sims has been active, and you can figure on saving $100/month tier once you have owned the full prim sim for five months (since you will pay a $600 transfer fee, and would have paid a $100 fee for a non-grandfathered sim. so you have an extra $500 cost, but a lower tier by $100/month).
And it's important to remember to use the LL approved transfer of Private Sim method of filing a Support Ticket to effect the transfer of ownership of used sims. NEVER pay a seller directly or you will not obtain full ownership rights at best, or may be scammed out of all your money at worst.
lexi