is watch chrono reliable?

I am in the process of buying some watches. I want to buy at a good price, a fair price for all involved.

This example I am offered 70 then 68, I decided to send it to a few local dealers and said if you were buy this off me how much would you offer they 1 said 57 and the other said 62.

I did some research on youtube some said deduct 15% from watch chrono and thats what you should be paying, not sure if this has any truth?

is there any other sites, I know watch charts, is that better? to tell me what I should pay ( I know they need commission but that should be like 1-2k over there buy in price not 6-10k imo) so yeah I guess how hard should you lowball and how much can you expect to get off a grey market dealer on average?