Ebay do not allow shill bidding.
If you suspect sellers are doing this, you just need to avoid them.
This is what Ebay say:
How do I report shill bidding?
If you think that another member is shill bidding, you don't need to report it to us. eBay has a number of systems in place to detect and monitor bidding patterns and practices. If we identify any malicious behaviour, we'll take steps to prevent it.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)