Hi
No direct experience of those but I used to be involved in a local petrol station group that had c-stores attached.
Talk to some existing shops locally to see what their experience is. Remember that the local wholesaler is likely to vary, so service will vary alongside it. Also see whether there are any "bad" shops locally that could taint the image of your chosen brand.
Find out what the ongoing fees are - advertising contributions, etc.
Remember there are also national wholesalers like P&H (who offer Mace from memory) & Key Lekkerland.
Once you get over a certain turnover, wholesale prices won't be much different regardless of which chain. Promotions may vary once you get beyond the standard Mars/Coke/etc ones.
Ask about over-riders and whether these are related to display agreements.
Find out what promotional support and help you'll be offered. Check with other local shops to find out how ongoing that it and whether the promises are likely to be met.
Check with your news wholesaler what their requirements are if your chosen location hasn't already got news.
Does your chosen location have potential for bake-off? Does it already offer national lottery? Can it get an off licence? All these help the customer count & margin mix.
Also look into the costs of a decent p-o-s system and the back office that goes with it. Again, does your wholesaler offer support and advice on this and do they offer files in a format your system uses so you can keep prices up to date.
Remember also that you'll need a decent turnover to make money after you've paid a manager (unless you like working 7 days a week, 365 days a year) met wages, shrinkage, etc.
Done well, retail pays well (ask Tesco).
Trevor
P.S. You may decide to go for a new store, build up the turnover (sacrificing profit) and then sell to one of the chains. This was done by someone locally a few years ago for a very nice profit.
Easy way to thrive onine during recession.