Not sure what you mean by "URLs are in red". Is this in your search results or do you mean files in your library? Files in the library in red mean they're not being shared.
On file sizes, be sure to check the bitrate. A file with a higher bitrate will be larger than one with a lower one. A higher bitrate should also mean better quality.
Files are sometimes cut off short and some have more that one version out, like a radio edit. Then there are the fake files, they're made to look like real files(same size, bitrate, ect) but they never d/load.
See:
Fake files showing up in search results