There's all kinds of general bad advice on Pinside.

"You should get a 'x' instead of 'x' game..."
Everyone's opinion on games is different. People should get what they like.

"I wouldn't spend '$x' on that game..."
That's nice...but you're not looking to buy or sell that game and don't know all of the details. People can spend whatever they want.

"Never have a game shipped..."
Oh please. Every game has been shipped at least once (from the factory). How do you think most games get moved between customers and some of the top restorers? They're shipped, both ways. And from respectable sellers, collectors around the world? Shipped. Now you shouldn't immediately trust and have a machine shipped from anyone, especially if they have no sales history, no reputation, no experience in shipping, etc. But a little common sense saves 90% of the issues from buying from a distance.

Some good advice I've seen that is worth repeating:

"Don't attempt board repair, especially on expensive boards, if you don't know what you're doing."

"Don't work under a powered playfield, IF you don't know what you're doing."

"Don't color bomb your playfield with colored LEDs in all of the GI."
Alright this one is just my opinion but I swear by it