How to Snipe on eBay
EBBay Bidders Sold on Sniping
Why sniping isn’t necessary (read comment)
Why eBay charges to use their API
Beyond eBay, Yahoo & Amazon auctions compared
Third party eBay apps
eBay API and Open Source Great comment thread, including:

The problem with ‘sniping’ is (as I see it) largely caused by people
failing to understand the auction process. Many people seem to put in
the minimum bid required to make them the high bidder and wait to see
if they are outbid. If they used eBay ‘properly’ they would just put in
their maximum bid at the start and if someone snipes them with a higher
bid then they haven’t actually lost anything. If someone tries to snipe
them with a lower bid then they still win.

EBay Service Fees

We understand that charging for API usage certainly discourages some developers from getting started with the program.

As
a result, we’re constantly reviewing data and listening to the
community to make sure our pricings and offerings hit that careful
balance spot between encouraging innovation and preventing runaway
costs.

Some developers have tried "screen scraping" eBay.com;
however, most of them have found that’s a bad way to build a commercial
application. The site changes every two weeks. That’s means your
application can break on a regular basis, and you will need to devote
time to repairing it. Additionally, it is against our terms of service
to screen scrape, so you could be shut down at any time.

In my
opinion, given the hourly rate most developers can charge for their
services, $500 a year is more than worth the time savings. However,
every developer must make that choice for themselves.

Adam Trachtenberg
eBay Technical Evangelism

Scraping EBay, a bad idea?
Official Ebay User Agreement

7. Access and Interference.

The
Site contains robot exclusion headers. Much of the information on the
Site is updated on a real time basis and is proprietary or is licensed
to eBay by our users or third parties. You agree that you will not use
any robot, spider, scraper or other automated means to access the Site
for any purpose without our express written permission. Additionally,
you agree that you will not: (i) take any action that imposes, or may
impose in our sole discretion an unreasonable or disproportionately
large load on our infrastructure; (ii) copy, reproduce, modify, create
derivative works from, distribute or publicly display any content
(except for Your Information) from the Site without the prior expressed
written permission of eBay and the appropriate third party, as
applicable; (iii) interfere or attempt to interfere with the proper
working of the Site or any activities conducted on the Site; or (iv)
bypass our robot exclusion headers or other measures we may use to
prevent or restrict access to the Site.

What others think about sniping

Is Screen Scraping legal?

Gartner Group’s Dataquest [2]
eBay Inc was successful in obtaining an interim injunction on the basis
of trespass which prevented Bidder’s Edge scraping eBay Inc’s internet
auction website. In the US, it is necessary to show a likelihood of
damage to succeed in an action for trespass. The court accepted that by
using over 100,000 automated searches per day, Bidder’s Edge Inc was
"draining" eBay Inc’s computer system resources away from legitimate
customers and that this had caused some harm to eBay Inc. The decision
has been criticised in the US on a number of fronts including on the
basis that the harm to eBay was not in fact sufficient.