Im surprised by the comments on ebay as well.
Always go BIN, never auction unless you're selling something not in your business like a leather jacket or something (and your business is selling car parts!).
If you're selling low priced items like mugs and you get an upset customer who demands a refund (for whatever reason, but within reason), or perhaps the mug was damaged in the post, just send them another one! dont get smart and say that you must contact royal mail to get compo etc. its world of hurt trust me. A mug costs about 88p, its nothing to just do another and re-send it. although if there is damage, politely ask the customer to take a picture of it and send it to you. It kinda reinforces the fact that it actually is broken. Word the message to them like "Just for our records to show Royal Mail, please would you send me an image of the broken mug?". The customer will do this straight away, thank them, then just send another. Ok so you're down a few quid but the customer will always leave positive feedback, its not like 20 mugs a month are broken. and also they'll return to you for more, ive had so many return customers purely through good customer relations. Always be polite, if you do get a negative mark and it's truly not your problem, contact ebay support and tell them. Ive had neg's removed because ebay support have seen that ive tried to rectify the problem to the best i can and therefore they see in your favour.
As for profits, some customers prefer to buy from a seller that is more expensive for the same product, again because of feedback. Be original with your items, if you have an idea then dont match the competitions price! Sell it at what you want to sell it at! If the customer wants it, they'll buy it.
Make your item page look like a business. Make a template but dont use ebays, they're naff! The more professional you look, the more sales you'll get.
Stay on top of questions from customers as well. speedy replies have resulted in many sales for me. If you're a day or 2 late with a reply then explain why and that you meant to reply earlier but .. blah blah... (make it up lol) but try to make them feel special, ebay customers are a funny breed and you'll soon learn this
Basically, you have to bend over backwards and jump through fire hoops with ebay customers, its part of what ebay is. Ive even spoken to ebay support and commented on that very subject and the person I spoke to agreed with me.
So, if something goes wrong, just sort it! dont get funny or you're guaranteed a neg FB.
Always be polite. If things go wrong and you need customer support to refer to your email with the customer with the problem, they will take a look at your attitude and base their decision on that, and I know that from experience.
Unless you're selling identical items, sell at your price. If you're selling identical items, stop and move on. Ive seen many sellers who have sold e.g. 80 mugs of a particular design like "I Love my Mum" for £4.00 and free delivery!!!! You might think that they sold 80 mugs, but look at the costs involved and that that seller has made about £1.00 each mug. (mug-88p, delivery £2.24, ebay fee about 30p, Paypal fee about 19p) in fact thats less than a pound! lol. why not do a better design and maybe even offer 2 mugs with free delivery, ebay customers love "free" stuff.
And finally, if you're shifting a good amount of items, pay your ebay shop fee by the week. Dont leave it until the invoice day (end of the month). My current fees are anything from £120 - £150 per month, pay it off at the end of the week. Your Account section will tell you what you owe on a daily basis, just pay it and suck it.
I say go for it...if you need anymore help or advice then just ask.
Happy sales

Dave