For 17K, your best bet would be ipad 9th gen. I'm not sure if you can get one for exactly 17k. Be little flexible on the price and search for 9th gen ipads on
olx.
Some of the tips I can think of while shopping on olx are:
1. See the pictures. Are they clear?, does the pictures show any scratches, dents, screen pixel isssues?
2. If point 1 is clear. go through the description. Some kind people do mention of why they're selling it. Try to guage the device based on the photos and the description.
3. Find the resale value of the ipad using
cashify (for the reference sake).
4. Next quote a reasonable price (which you can extend to couple more thousands if the buyer is willing to negotiate). Guage the price on the condition of the device too.
5. If both of you agree on a price, ask him to send you the model number to confirm the authenticity of the ipad.
6. If you get one, check it. If not, check for it before you exchange money after meeting the buyer.
7. In no circumstances, transfer of money should takes place without physically inspecting the device and confirming its condition.