The "line" may be very fine indeed:

In "Overall conclusions":

"At the risk of defining a normal behavior as abnormal, though, it’s important to be aware that there may be a subgroup of 'Extreme Collectors' who meet all the criteria of hoarding but have not been diagnosed. These avid collectors may go undetected among the collecting population because they seem to be engaging in the same behaviors as the average collector."

"Just because you enjoy collecting, and may even have a few stashes around your home or office of objects that mean more to you than they do to others, this should not be a cause for alarm. However, when you, or someone you know, starts to show those extreme collecting signs (#3 and #4), it may be time to seek help."

https://www.psychologytoday.com/blog/fulfillment-any-age/201207/4-signs-youre-extreme-collector