Everyone is going to have their own opinions on this subject. It's going to be very hard to make sense out of it all once a thread like this is over.
If you want to sell domains fast, then you have to be a trend chaser. You have to be good at spotting internet trends and register good domains within that trend and immediately put them up for sale. You never want to hold on to a trendy domain as the domain loses all or most of it's value as the trend matures and dies. there are exceptions to every rule, but that is the rule. You have to be quick to register, but not so quick that you make mistakes and register a bunch of trendy domains that suck. But it's like high frequency trading - there are a lot of seasoned folks out there using a lot of tools to find $$$ domains quickly. But this is one way I know of to make fast sales.
Also, you may want to consider developing some domains in order to increase their value and hasten their sale. Just because a domain has a nice, brandable name, it doesn't mean much in many cases. An example would be a domain I own e/s/m/o/k/a (dot) com. It is a very brandable domain in the ecig/vaping genre. I own it because I had planed on developing it and going into the ecig business back in 2013 with a "buddy". I was going to start a line of vaping products for older smokers. But my "partner" bailed on me (he was going to be the $$$ investor in the deal). Then a year or so later my state made it very hard for folks within my state to get into selling vaping supplies by imposing super-high taxes. So for these and for various other reasons I did not pursue it.
Point is, it's a very brandable name in it's niche, but that's all it is. I will get nothing or very little for it if I tried to sell it. At this point, I have spent roughly $48 in reg fees on it and I am doubtful it will sell for a profit, if it sells at all. What I should have done (had I had a crystal ball) was I should have tried selling it back in 2013. It still would have brought little profit, but probably more than today.
Of course, in order to develop a domain, you have to have that skill. Otherwise, you will have to pay someone else. There's nothing wrong with paying a developer, but obviously you can't be doing this on domains that are not going to bring at least X,XXX after developed.
DO NOT USE WHO IS PRIVACY!
I have gotten offers for domains that had whois privacy and have sold one. Whois privacy does not stop people from contacting you via email. It's just that they cannot see your email address...it's masked, like hsdf9834ljsfdo987345lijdrf90873w4ierdf8974ewifdg908.whoisprivacyservice.com. They only know your real email if you reply.
Is it best to remove whois privacy from a domain? I don't know. There are many opinions on this matter. Some say it increases their inbound sales by 10%, others say that the increase in sales, if any, is negligible. I think it depends on the domain and your portfolio. But if a buyer is serious about buying a domain, that buyer is not only going to send their offer to the whois privacy email address, but they are also going to check the domain's home page for a "for sale" landing page and a contact form. If a buyer is only surfing whois data, then that tells me they are not really that serious about buying a domain and may probably be a reseller (which means you will get less for your domain). I'm not against selling to resellers, but I'm also not going to sell a domain to a reseller that I think will garner 3X to 5X more if I wait a bit longer.