Check the accessories that were mentioned on the forums, also verify that which accessories comes with the new one and if any thing is missing ask the seller about it. Check the original body of the phone(specially if its Nokia). Check the seal of the warranty even if the cell's waranty expired. If phone is in warranty match the IMEI number of the warranty card and the phone. Check the incoming and outgoing voice with and without handsfree. Check the volume of the ringtone speaker. Check LCD contrast. Always Make a real call from the phone and verify the incoming and outgoing voice. Attach the charger and charge the phone for 5 mins Thoroughly check the menu, Check Camera, Check Video/Audio Playback, play with the phone,turn it On and OFF couple of times. Remove the battery for couple of minutes and reinstall it again to verify the health of the battery. Ask the seller why he wants to sell, is there any problem with the cell(Even if cell looks like a new one). If a locallly used 1 or more than one year old cell phone looks like a brand new one ,check it more carefully,its may be painted. To check wether the phone is painted or not, carefully examine the edges of screen ,the speaker and mic place you will defintly find some evidence of spray paint.one more thing if the surface of the phone is a little bit rough or grainy slightly scratch the phone's paint with your nail ,if its painted the pain will be removed. To verify wether its repaired or not. - Check the warranty seal. - Examine the all Screws very carefully if a little bit paint is removed or all the screws are not alike then the set is opened. - See the edges of the phone,the line between the upper and lower halves of the body. Press phone slightly if there is a little bit play between the upper and lower half then the set is may be repaired.