First off I bought my 300PDS and NEQ6 Pro from a well known on line auction site so I can't comment on the seller, only the scope.
Getting up close and personal with one of these you can not help but note it's size, probably about the biggest Newtonian you can put on an EQ mount. So I'm a bit shocked at how many people I know that have bought these unseen and then been overwhelmed by them (this is how I bought mine). But it is hardly surprising since neither the description here nor on Skywatcher's own site gives any real feel as to the physical size of this beastie, individually they seem rather innocuous but put together all in one place the whole is certainly greater than the sum of it's parts. I have posted some photos of mine here for scale.
As per the pictures with the mount tripod at it's lowest setting, the puck of the NEQ6 mount (the place where you attach the telescope to its tripod) is over a meter off the ground. Add to this the fact that while the main mirror is 305mm (12") the actual tube is 350mm (14") in diameter or more practically, I can just about get my arms around it in a bear hug (not that I carry it this way)!Slewed horizontal for turning the eyepiece or balancing the tube is level with my chest. In addition the tube weighs 26kg and is unevenly balanced toward the mirror end (as all Newtonians are) so putting the tube on the mount could be tricky if you are either vertically challenged or have back / lower joint problems. The mount itself is also quite heavy, Skywatcher's site have the actual figures but the tripod is something like 9 kg and the EQ6 is around 17kg (plus you need 4 x 5kg counterweights for a 300) so it's no light weight, pick your observing spot for the evening / morning with care because you are not moving once set, also bear these weights in mind if you have any condition that prevents you from moving heavy items any distance.
Once set-up this scope really comes into it's own, the NEQ6 mount is certainly heavy enough to deal with this monster and the inclusion of a goto system to help find stars is a real bonus. The most recent versions of the SnyScan firmware offer a polar alignment without polar scope option, this is probably OK with smaller scopes but even after balancing I would not recommend using this utility with a 300 as this seems to put an awful lot of strain on the Alt/Az adjuster bolts.
Optically these are superb, they are excellent scopes for finding dim deep sky objects (galaxies and comets) and give fantastic views of large nebulae, the planets and the moon, for both of the later you may need an ND (moon) filter I find Jupiter to be very bright unless seen through light cloud and for the moon I would strongly recommend a double polariser filter otherwise the view is almost painfully dazzling (this scope is all about light gathering). The two speed focuser is also a winner here, all scopes jiggle when handled and this true for the 300 on the NEQ6 mount, but the dual focuser helps a good deal here, you can use the fast focus to get your object roughly in view and then only the lightest touch is needed on the fine focus knob which drastically reduces shake. The 28mm LET eyepiece that comes as standard gets mixed reviews elsewhere, all I can say is that as an introductory 2" eyepiece, it's pretty good, the centre 70% of the view is usually sharp with comma and other optical irregularities only creeping in gradually toward the edges. It does afford some excellent wide field views and while contrast could perhaps be better, you will probably be looking at some expensive 2" Eyepiece upgrades to improve on the supplied one.
Finally established wisdom says that for taking photos you need a mount with 2x the capacity of the tube, the EQ6 is at full load carrying this tube. This said I have had some good 30-90s exposures using this set-up in still conditions, if you are wanting to use a 300 PDS for full autoguiding etc you are probably not looking at this as a package in any case as you will be needing something like an EQ8 mount.