I've just been looking into this so will throw in my thoughts.
We've used streamline for years and it used to be that a mobile card reader was a huge cost so we simply have one based at our office - customers phone up (with engineers hands round their neck) & I take payment a card holder not present transaction.
Today if I now get a mobile card reader from streamline the fee is £27 pcm.
There are also transaction fees and for most cc they are almost 3%.
But the important point is debit cards have a really low fee per transaction regardless of the size (I can't remember how much but perhaps 70p).
So - Taking payment by debit card for large amounts is better via streamline or getting direct bank transfer.
BTW, we also tell customers that there is a 3% addition charge on transactions paid for by credit card - but we only apply this to large sums not the £50 jobs.
Only one person complained that we were profiting, she claimed credit card fees were more like 2% so I called streamline and confirmed they are higher. and I pointed out to her that we are also pay an additional monthly figure in order to take credit cards for her benefit not ours. We are still slightly out of pocket over all to streamline I believe, those 3% charges do not cover all the cost. Most of our customers do not pay this way.
BTW it is worth calling streamline - they do reduce those fees if you ask them too, it only a small amount but every little helps.
I'm not sure whether I will go for streamline, worldpay zinc or do nothing.
I am hoping to replace taking cheques - so theoretically customers will pay by debit card, so streamline is the right choice for me, but I'm not keen on it costing me £324 per year.
Thanks for this thread and the link to worldpayzinc