You can't send elf force to people unless they're masterbelt or any of the belts higher than masterbelt. Unless it's a no-qi item, but people usually don't sell no-qi items for just 1k or something since it's way too low priced for a no-qi item.
I got a tip if you want to avoid scamming and to make sure the salesman is honest; ask him/her to make a shop at the Market (unless he/she already have one) and tell him/her to place the item in that shop and ask for the link to the shop.