Thanks Guys for responding and the welcome.
You are welcome.
What I am looking for is, what mistakes did I make.
Perhaps none. It completely depends upon what you paid for the items.
Firstly what would you value them at, ballpark? What would be a realistic price?
As I said earlier, without seeing the actual stamps, rather than scans, it is impossible to tell. I thought originally that the Bridge may be a crease. Scuzz has now put in my mind that it might be a (well) repaired tear. This would substantially change it's value (downwards) if it was a repaired tear.
Secondly and you have identified a couple of errors, such as creases, short perf and badly stained.
Being a newcomer, what are the error's to look for? What makes a $10k stamp become $8k in value? Basic things to identify a reduction in the price. The wallet is staying in the pocket for a while due to inexperience.
This could depend on so many factors that it is virtually impossible to answer briefly.
For a relatively easy to acquire stamp such as the 5/- Bridge, or the 6d Kooka that you have as an avatar, very well centred, perfect perforations, fresh unhinged (or very lightly hinged) gum, nice cancels on used for a start. For extremely rare items, you will not find a bargain on eBay unless you are exterely lucky. The market sets the rate.
There are too many variables.
Knowledge, experience and research is the key. Talking to dealers, the people on this board, subscribing to auction catalogues, buying trade and retail magazines, looking at dealers price lists, seeing how dealers rate quality as opposed to "normal", will teach you a lot. You are going in the right direction by asking questions.
Also, bear in mind that we cannot give investment advice on this board.
I started a thread a while ago about when Australian decimals were the flavour of the month. The first decimal series reached around the $350-$400 at it's peak. You can now pick up as many sets as you care for for around $25.00 each.