Cheaper to buy than build is definitely the rule, not the exception. To successfully buy said done car, I believe you have to have done one or the story ends badly. Do some of the nasty jobs listed here and you’ll be checking the trouble spots first before going cash for keys.

Of all the many things involved with restoring a car, it is hard to pin down any one thing that is the worst that everyone will agree on.
What annoys one guy may be an attractive challenge to another.
I hate waiting on someone else to do their job so I can do mine. One example, Machine Shop services. Some places don't seem all that busy when you drop your stuff off but somehow you still get l-o-n-g delays for the completion of your stuff.
I'm a decent bodyman and a mediocre welder but I can make my way through metal replacement and body work.
Finding parts for many of our cars is a matter of luck and timing. Many one year models make it hard to find fenders or grilles that are not reproduced.
1966-1967-1968-1969-1970 A body cars all use a different fender for each year.
1967-1968-1969-1970-1971-1972-1973 Chargers also use a different fender and grille for each year as well. Finding that needle in the haystack can be extremely difficult.

I have fun reading this kind of treads, Just a few things I've noticed over the years,

Taking a car apart is easy.
Taking it apart so it can be reassembled is harder.
Taking it apart so some of it can be reused is really hard.
I've never seen a body guy, or mechanic that thinks the last guy that did something on a car did it "the right way".
Most body guys and most mechanics will tell the customer they they are "going to fix it the right way, not like the last guy did."
The only difference most people see between a $50 part and the same part that is a $20 part is $30 more money.
Most people can't understand how its going to take hours to "Put that little part in there."
Everything on the car worked until you did that unrelated thing to it, now they expect you to fix this unrelated thing for free.
Most people believe your shop's hourly rate shouldn't be any higher then their hourly pay.
They watched that restoration show on TV, they know its only going to take a month to restore their car and they know your going to put $30,000 of what your charging them into your pocket.
Doesn't matter how many months you have been working on their car, if you expect to be paid some labor money, you intend to rip them off.
It doesn't have to be "show quality" until after they have paid you.

Whats the worst thing to do when restoring cars?

To me it’s setting a completion date and a total budget. It will likely take longer and cost more.

So now I take my time and try to enjoy the process

^^^ Words of wisdom right there and I agree.
I gave that advice to a buddy who decided to restore his Dart a few years back, and he still thanks me for that.
Also agree on how previous experience helps when looking at a "done" car.

I can only echo what others have experienced. I don't like electrical. I dont have the skill set for body and paint work. Crappy restoration parts and crappy service and or quality when you do farm something out to an alleged professional.
Not bagging and tagging and photographing every single thing is bad. Made that mistake a couple of times. You think you will remember but you won't.

In my eyes, the worst thing to do is paint the bottom side of the car when it wasn't painted in the first place. That is not restoring, it is improvising.

Sending the car far away and then having the guy hold your car because of stories about the wife blah blah blah.

Get into drag racing so you have to fix it every week, and it never really gets done.

"if it ain't broke, keep fixin' it til it is !".............

The worst thing to do?

Fight with the shops and ppl to finish or make things correctly.

One common thing not mentioned that many do is rebuild the motor first then leave it sit for 20 years

or tear the car apart and leave it sit for 20 years.

Not drive it when you are finished.

that too !

Body shop jail

X2..."Licensed Mopar Restoration" labels have to be the biggest farce in this industry.

Licensing is just a profit opportunity for the licenser.....it doesn't mean the part is any good, it just means part of what you pay goes to support a corporation who isn't
directly involved in making parts you want anymore.

and doesn't care about anything except collecting the bux.

In the last 25 years IMO, the only company that I am aware of that is still in business and produced top notch parts is Trim Parts. In a few instances the quality was better than NOS or originals. Rare parts is another