Heiho,
no need for testing ^^
Vendors in Norm Act1 can only sell up to iLvl12, regardless of cLvl.
Vendors in Norm Act2 can only sell up to iLvl20, regardless of cLvl.
From Act3 on it'll be difficult to gain a plain sword, because the vendors sell magical only stuff, since from iLvl25 upwards there's magicals only. But you'll need an iLvl26 sword to get four sockets, so even if you rush through the acts, you must be cLvl21 to get an iLvl26 item (Act3 vendors sell up to iLvl28).
You may see some plain items even in act3, but not when you're cLvl21.
no need for testing ^^
Vendors in Norm Act1 can only sell up to iLvl12, regardless of cLvl.
Vendors in Norm Act2 can only sell up to iLvl20, regardless of cLvl.
From Act3 on it'll be difficult to gain a plain sword, because the vendors sell magical only stuff, since from iLvl25 upwards there's magicals only. But you'll need an iLvl26 sword to get four sockets, so even if you rush through the acts, you must be cLvl21 to get an iLvl26 item (Act3 vendors sell up to iLvl28).
You may see some plain items even in act3, but not when you're cLvl21.