Sort:  

they use other people's voting power to vote on your post (if you buy vote)
and use your voting power to votes on other (if you sell vote)

In short: you can buy votes for your post or sell your votes. Both ways get more ROI for you.

Coin Marketplace

STEEM 0.19
TRX 0.18
JST 0.033
BTC 89688.42
ETH 3103.55
USDT 1.00
SBD 2.80