450 comics isn't a motherlode but maybe a babyload.
We can't all be Donut or October or (whoever) and find a guy with a van full of SA comics ready to unload for cover price.
To be fair, a lot of people put in a LOT of legwork into getting 'lucky' with these comic finds. Of course, sometimes people get lucky too.
Also, I'm guessing the best stories will never be told... I know I'll never tell mine...(and no, I didn't bilk an old widow or anything).
Here's the key:
1) Always be on the lookout. Always. You never know.
2) Let all of your relatives and friends know that you're always on the lookout. All of my cousins across the country know to call me if they see comics anywhere.
3) Don't be a person_who_is_obnoxiously_self-impressed to people. Douchiness tends to radiate to muggles.
4) Offer a fair price.
5) Have cash.
6) Buy it all. Don't offer to cherry pick.
7) Be very very very ready to bail. If the seller's asking price is ludicrous, smile nicely, say "thank you for your time" and pack up your stuff. You're only out your time, and you will be amazed how quickly that ludicrous price comes down.
Good advice, while I don't buy many collections. I always look and put out feelers.
I second that good advice.