That means dev themselves put first buy order and sell to themselves in order to raise its price, right?
If nobody else had interest in trading the coin, yes the dev could easily manipulate the price.
Like? what other ways?
Have you never participated in an altcoin airdrop? Giving away free coins to the community is often called
airdrop. If you look at the altcoin announcement section, most new coins aren't a mineable coin. That's the trend of the past. The current trend is people creating a token on Ethereum or Waves platform then airdropping them to the community. Here's some example (randomly selected):
[🌟Airdrop] ✅ ⚡ ApexCOIN[XXX] ❤ Based on Blockchain Technology🌟⭐⚡[ANN][AIRDROP][ICO] BITCOIN9X (BTC9X) - Future of Crypto Payments ⭐⚡So how? What ways? They usually require people to register for the airdrop via an online form + doing some simple task like following their social media, joined a telegram group, etc. Please note that most of these airdrop tokens are just worthless altcoins.