Im thinking about selling one bitcoin @ $5k where should I do

You countries fiat / BTC exchange probably offers the best rates / lowest fees.

>>3059630
would tether be safe bet if i'd like to buy back

>>3059703
Yep, Tether has the lowest fees, is the fastest to buy / sell and lets you keep your money on the exchange so you can act quickly instead of waiting for transfer times.
Whenever you are shorting use USDT.

>>3059743
could tether get fucked with sudden price change?

>>3059918
Lots of people have tried to fuck with tether but the all time low is 92 cents and the all time high is $1.04 so it's pretty good at stopping that shit.
https://coinmarketcap.com/assets/tether/

There are heaps of coins that are meant to stay at $1 USD but tether is the only one that actually works.

>>3059617
sell it on coinbase they are totally trustworthy and reliable BELIEVE IT!