Certainly it's fair. I snipe bid all the time, I do it manually though. I don't use the bidding services, but it's not because I think using them is unfair. I don't use them because I'm cautious (maybe overly cautious) about trusting them with access to my account.
Sniping (whether manually or through a service--there is no difference to other bidders) is a defensive tactic that is the best single defense against shilling sellers. You have no need and no right to know anything about my bid to be able to bid effectively. If you can't decide your true maximum to bid in 7 days why do you believe you will do a better job in x minutes while in an emotional state over being outbid? On the other hand x minutes is plenty of time (particularly if it is extended by another x minutes as most auction extension proponents want) for a shiller to drive the price up to your supposedly hidden maximum and then retract/cancel the last bid if s/he goes over.
eBay's auction format is what makes it fair to those in up to 24 timezones with different work/sleep/computer schedules. Anyone can bid what the item is worth to them at any time and anyone can set up with a third party (there are reliable and secure ones which offer free limited use) to submit that bid in the last few seconds to get the defensive benefits of not having one's hidden maximum out there for others (again, including shilling sellers) to probe or otherwise base their bids on. Making it so those who are able to be there to react at the end have the advantage is what would be unfair.
