I had collected for quite awhile before deciding that I would only collect coins approved by CAC (except in special situations). The decision was based on several reasons but one in particular. I bought one gold coin and did all the right things. Worked with one of the best dealers in the country. Viewed it in hand. Of course it was slabbed. Great eye appeal. Price seemed very fair. At some point I send my first 20 coins in to CAC and I "knew" this one would sticker. Others did but this one came back with a note saying "puttied"! Everyone is different but I did not want a puttied coin in my collection. I also realized what I was doing needed an added layer of scruitny--CAC. It didn't mean I still wouldnt view coins myself, look for eye appeal, work with dealers, etc but CAC became a requirement for me.
So I thought going this route would help with avoiding coins that were doctored. But there was an added benefit to my new criteria--- I learned patience! I collect gold and proof gold. CAC is really tough on these. Before if there was a tough date and it came up for sale I would usually makes excuses to buy it since I knew that date was hard to find. I would say things like "well it's not all there but it's better than nothing" or "well the price is a bargain" , etc. Next thing you know you have a bunch of coins that are exceptions.
When I switched to CAC only I quickly learned that the gold coins I collected simply did not show up very often with CAC approvoal. I was tempted regularly with non CAC examples but held firm and waited. I learned patience. I know because of CAC I avoided alot of mistakes. Best of all, taking my time I built a collection with no compromises.