Doing the markets is a good start.
You will get to see where you are at with other collectors and also dealers,when you goto the markets people will get to know you are their.
Start a facebook page just letting people know what you have and where you will be at the markets or even a shop.
Depending on what sort of cards you are selling sports carnivals,if you are selling N.B.A see if you can set up a 3 by 3 metre site at one of the games if you do this you will need public libalilty insurance.
With your insurance find someone who will let you pay month to month because it can cost from $1500 a year and thats startings so if you do a company to do that it may only cost you about $130 a month and make sure your insurance can be used anywhere within australia just in case you find a shop to add to your insurance if you do just the markets a lots of markets do have their own insurance.
Remember if you do look at a shop it is all about location,location & location.
You have a ebay user I.D when doing any listing have your details if you are at the markets or shop,by having a ebay store paying $50 a month listings are 0.20 for by-it-now for 30 days by having your details on their for example last saturday i had someone ring me from the gold coast about something i had on ebay my shop is in Ipswich they drove up to buy the item off me.
Business cards or flyers if you are at the markets,a lot of people will walk pasted but when they have seen you a few times they look and go this guy is here to stay which is what you want.
Aline yourself with a larger dealer that way if someone asked you for something lets say its a $25 card you might get it for $20 including postage then you sell it for $25 does not sound like a lot but if you help them theirs a good chance they will help you.
Ok now for a shop Look around remember if you find somewhere that you like dont signed a lease someone i deal with in sydney is opening a shop at a cut price rate of rent $1000 a week and yes that is correct.
If you find a shop you like have a look if their is more than 3 shop empty the ball is in your court to get the cheaper rent.
Instead of signing a lease get it for month to month for 6 months let them know you are wanting to open a shop otherwise they will think you just going to be here for 3 months then go.
If their are fixtures you need look at buying them second hand to start with or even better make them,some of the best things have been made by people because they know what they want.
The thing about a lease is if you are paying $1000 a week your bond will be three month which is $13000 bond plus you will need 2 months rent so which is $8666 plus bond $21666 before you open your doors then theirs electricty,phone & internet.
When you look at what i have just put about sounds like a lot and it is.
By going into month to month no bond but you will need your rent paid in advance.
Now i can tell you,you can get rent cheaper just look around.
If you go into a shop have a fridge sell drinks out of it so people can buy them that come into the shop.
Know where public transport is for people to come to your shop,just incase someone is traveling a fair distance you can let them know so they can get home.
If you are near a taxi rank have a urn and offer free coffee and tea to the drivers the reason for this is a bit of extra security as they will want to look after you and also how many taxi drivers have kids they walk pasted your counter and go the kids have been good a nice treat for them thats not high priced.
Email all card companys tell them of your plans and ask for promo cards to give away.
Know where their is a carpark around so people can park safely.
Here is one that is a must know,know where the food places are around you what they sell because if you do this people go wow yep i can go 150metres down the road around the corner and pick up my food,when doing this make sure you have extra sits so they can bring it back and have it at your shop.
Unless you have a fair bit of money don't advertise school newsletters,notice boards are a way for people to see you.
When opening a shop dont beleive people will not walk in and want to see what you are doing this is my second shop now and they did that in both shops.
Offer a discount to any local clubs just a way to get noticed.
This is just a small part of things to opening a shop and keep it going.
Have a plan from start to finish while you have a plan you have a direction.
Good luck.