Top 10 Snafus to avoid when building a good rig

OK, I'm sure we'll come up with more than 10. Whatever.

Maybe I'll compile the top 10 once we get a few.

I'll start with my #1: avoid putting speakers that are too big in a room that is too small
Davt, I confess -- guilty. Mea culpa, mea culpa. I often refer to my set-up as a rig. Where's Audiofiel when you need him??
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Trusting the advice of "dealers" who you assume know what they are selling and how it is supposed to work.They will walk all over you until they squeeze the deal they want and won't stop until they intimidate and humiliate you into buying.Make sure you ask every question you can think of and drain every ounce of patience out of these weasels,then buy it used.Avoid dealers with names in the business like Ultimate,high end,upscale and the like.These guys should be selling cars.If they put you on hold hang up.If you are looking for advice see a priest,if you want to learn about audio make friends,join clubs,read and read and listen and listen.Never assume a dealer knows anything about audio because they sell it.
Top 10 might be too much but so far only top 5 found without placing in particular order I'd like to finalize the following:
#1 from Hotmailjbc >>Forgetting to enjoy the music<<
#2 from Ahendler >>Listening to others opinions rather trusting your own ear<<
#3 from Schipo >>Thinking that paying more will give you better sound<<
#4 from Almarg >>Attributing sonic characteristics to components or cables that are in fact the result of INTERACTIONS between those components or cables and what they are connected to, and/or other parts of the system<<
#5 from Marakanetz >>Building system for a specific type of music<<
Never, and I mean never, buy a used turntable unless you can go pick it up and have it demo'd to be fully functional and operational, including the cartridge checked out with the 'track record', before you hand over the cash.