Virtually all my gear was bought S/H from the classifieds on here and I've never had a bum deal and saved a shedload of money!
Also since I'm buying from photographers I can be fairly certain the gear has been well looked after.
Apart of course from making sure they also have good reports and a decent feedback score.
As always - it depends.
I've had some good secondhand buys on here, but then I've also some poor ones as well. Items missing parts that were 'forgotten' to be mentioned, a body that I suspect had bent/straightened pins on the CF slot as they broke the first time a card was removed requiring a whole new main board.
I've bought and recently sold to
MPB. Whilst you don't get as good price as selling yourself, it takes away all the hassle of selling, provides a quick way of obtaining the money, providing you're fair with your appraisal.
I certainly wouldn't recommend selling through ebay, there's too many fraudulent buyers claiming the item wasn't as advertised, didn't arrive etc. You've then got th eissue of postage, packaging.
If you can sell locally with a face to face meeting and cash thats probably best - local facebook market place? However I tried to sell a 70-200 f2.8 IS lens locally and the buyer got very nervous about turning up with cash!
So a trade in works at times, for speed, safety, no hassle, but you get a less than if selling private. There's nothing to stop you getting a quote, in fact
MPB make it very easy and fast, so it's worth it to give you an idea.
Only you can decide if that's where you value your kit, your time and the timescale you want the cash in
exactly this, get your posts up to over 25 and advertise here, price them fairly and you'll get more than you would by trading. I may even try it myself soon. 
