my n900 camera does not work
i mentioned here

the physical lock key does not work

also now i am facing some screen issue mentioned here in the post #6

now i am planing to get another one

in my city there are too many shops who are selling N900's but no one gives any type of warranty. can you help me out what are the things i should check before buying it?

You could install healthcheck application before buying and go through those screen to check everything is about working.

Maybe you do not have network access on the phone you are about to try.
If you have microsd-card, you could download the needed healthcheck.deb file and the packages it depends on beforehand to the card. Then just insert the card and install the files from them with dpkg -i

here in egypt many sell it too but most of the devices have changed the usb socket so take care of it
also they decisive people by telling them that the device is new by changing the screen protector and changing the whole plastic cover so to make sure you can open the back cover and see if it is scratched or not..
another thing make sure that the screen is not scratched .. remove the screen protector and check it
finally please mention its price in dollars
btw i have got a new one in the box from couple of monthes

This can't be that difficult to answer for yourself, now, can it?

Make a list of all N900 parts you could live without.
Make a list of all N900 parts you could not live without.
See what overlaps. Presto.

Typical items for me to look for (and that have been mentioned in threads around the board only a couple of thousand times...):

USB port. Does it wiggle? Don't buy.
The screen. Lots of damage? Don't buy or replace the screen.
Do all the keys of the HW keyboard work. Does the KB slider wiggle?
Was the device overclocked? Above 900 Mhz? Don't buy.
Bring a SIM card to check if it works.
Run fsck -a to check for errors on the filesystem.

Etc.

Did you already tried to reflash your device?

i have not reflashed it yet (i dont think it will work) how ever i would backup my data and will reflash it within a week

@davdav
i should be around 200$
and...
i have a few question

1>how do i find out that usb socket is changed?

2> is there anyway i can find that whole plastic cover is original or not?

3>As anthonie says
how do i know this?

4>why should i not buy if it was overclocked?

5>as anthonie says

i tried it in xterminal but nothing happened it says "fsck not found"

check this thread. it has many tips regarding buying a used N900. Buying N900 tomorry

i think its too much for it .. i have got my new one for about 250 $

you can notice the screws under the cover it may tell you if the device was opened before or not and if it was ..then you have to know that the usb socket had changed (As it is the most common thing)

get your n900 (the old one) with you and compare the colour may be its brighter or darker than the orginal one