If, despite this, it's still an issue, there are lots of bot algorithms that can drive up volume and/or reduce the spread. These sorts of market maker bots - or, for that matter, regular ol' human scalpers would remove the problem.
Finally, the Blocknet will support an entire economy of services; liquidity will be, at best, an initial problem.
the same market maker bots are working currently on all exchanges (i ran one on polo) and they dont solve the slippage problem.
why do you think that this would be better with your p2p-exchange?
seriously: i dont want to downtalk your project. i just want to see if it is useful (atm i dont think so: but PLEASE convince me

If exchanges are useful to you (and by the sound of things they are) then why would the Blocknet somehow not be useful, especially if it massive increases usage of coins, thereby reducing slippage?
Also, the slippage problem only applies to transactions above a certain size. Microtransactions for services won't be affected.
So *even* if the Blocknet doesn't increase volume and liquidity, there's still no problem for microtransactions (i.e. service fees).
i like your exchange: but there are already other ones - and yes even p2p ones like nxt.
your project is intersting to me because it allows me to use other coins features without actually holding them (eg the SMS send feature you mentioned).
but this will require an automatic conversion from and to my base currency. this two exchanges will cost me money (spread) as no one will have a sell and a buy order at the same price (it isnt even possible btw as they would match each other)
so i only can see this as an additional fee from the user perspective and as a way to get money from a market maker pov.
and atm the spreads in altcoins are really BIG ( i have seen way more than 20% loss just for a back and forth conversion)
if you have an incentive for a market maker to make the spread as small as possible this wouldnt be a big issue: but i dont see any (i mean any more incentives as with the current exchanges)
I think that an important point with regard to this matter is that its significance depends entirely on the service in question. Services that only require a one-way transaction will not have this as even a potential problem.
Equally important is the fact that the issue is entirely addressable by the design of any given service (i.e. by a coin, not by the Blocknet), and these services have not been designed/optimised for the Blocknet.
For example, if a service requires that coins be returned to the client, then they don't actually have to be exchanged, and so an escrow service might work better.
This would eliminate slippage and thereby present a competitive advantage to any service that offers it.
The point is that you're worried about something that is (a) readily surmountable and (b) hasn't arisen yet. You're pre-empting an issue and then worrying about it as if it's a real problem.
It isn't. In a free market of coin-based services, there'll be competition on a new level. Coins will have no problem inventing clever ways of rendering quality services and rising to the top of the pile.