Take a look at the hair and the eagle breast feathers. The hair is not particularly detailed, and the eagle breast is pretty bare--feathers should be well defined. For a proof, this is a very soft strike--it looks more like a business strike that is PL than a real proof IMHO, and I have seen other pictures of it.
This isn't a horrible strike for a business strike...but even for a business strike it's not overly strong. For a proof, one would expect a stronger strike than this.
All I know is that I almost passed on buying a few DL coins because their scanned photos don't do them justice. I've taken leaps of faith on purchases from them before based upon their return policy. I have yet to ever return a coin from them and have always been happily surprised by how much better their coins look in hand than in photos. That's just my experience with them. Every photo I've seen has looked poorly struck and none ever were. I've even started a thread in the past asking advice on a coin based upon 2 coins with exact same grade/CAC. Everyone suggested the coin with the good pic from Heritage. I went with the bad pic from DL and was very very happy. And I saved a good 20% between DL and Heritage. I have always got DL coins at 10-15% below asking with a simple phone call. If you are worried this coin might haunt you later if you don't buy it, I would get it in hand then make the decision to return or not. Good luck whatever you choose.
I didn't now that...I have never spent much time studying the Morgan Proofs (unlike the business strikes), so I don't know the strike characteristics from year to year. I'm also at work surrounded by no coin reference books.
This really depends. I have an 1887 proof Morgan that is a super strike--they tend to be quite variable, unfortunately. Normally, Philadelphia mint coins are more consistent in strike quality, especially the proofs. It is not so with proof Morgans. I own 1883 and 1884o Morgans that are business strikes that have better strikes than this one (those two dates are notorious for being inconsistent from a mint famous for light strikes).
To tell you the truth, I am not exactly sure why this is and wish that I could provide the reasons/causes, but even a quick comparison/sampling of other specimens should show weakness is not uncommon for the date. Which is why I was sure to add "(date)".