Offered 10k for a 35k property (winston salem nc)

This is my 3rd offer... i have a family that wanted to go back to California and had a 35k property which they said was worth 45k.  I have not seen the inside but the comps was about 35k... so i offered a soft pass of 10k they called me crazy, so i offered 15k and they said if i cant offer 35k dont call them back and hung up on me...  when i was talking to the son i was trying to build rapport but i was kind of talking to many people cause i was on speaker...  what could i have done better?