Both spamming and shitposting are bad habit and should be prohibited. But I think Spamming is worst than Shitposting. When yyare posting something irrelevant and off topic that means you are doing Shitposting. But for spamming you just spreading your probably fake message to everywhere and breaking rules.

Actually shitposters are being paid because they just want some workers who just need to spread their scams. Because no genuine project will hire shitposters. And they don't care if your account is getting banned or locked. So never do this types of jobs and always be effective and creative.