Heres my experience of FBA - some items really benefit from being in FBA - usually business type purchase items - so not a personal purchase. Small items as well as the carriage costs are good.

However personal purchase items have a much higher return rate and I mean a MUCH higher return rate and when you then have to pay to get an item returned to you it makes the positives of FBA soon become a negative. You have to remember Amazon buyers send stuff back and they send it back in shocking condition and Amazon refund them - not only that they lie and say the item is faulty even when its not so they get the item returned to Amazon for free - this then goes against your stats for selling defective items. If you then get an item that starts selling well you may find Amazon start to sell it under your cost and you get left with loads of stock in FBA that then start to accrue storage costs unless you pay to take it out or reduce your costs and potentially make a loss. My advice is unless you have a good niche product or a product you have bought through proper channels at a really good price I would think twice about putting volume in there. Amazon can also put a stop on your products and proving authenticity can be a long drawn out affair which still may result in them not letting you sell your stock ! Amazon is a fairly faceless organisation and getting help is hard as theres so many autonomous replies to things.

You need to do more research but theres some research you just cant do I would dip my toe before jumping in