Question about detecting shilling

[itjclarke]

I've seen shill bidding pop up often in various threads. It's clearly a problem, and seems both hard to enforce while fairly simple/easy to execute.

My question- where do you draw the line when suspecting shilling is occurring? I'm viewing an auction now.. a bidder with 800+ feedback, shows 38% bidding activity with this seller. The bidder has bid 15-20 times on this single auction.. each time inching the price up in $5-$10 increments, but never taking the lead. Rather than bidding in round amounts ending in $0 or $5, their bids all seem to end in $2, $7 (like $422, then $427). I won't name the seller as they're feedback is impeccable, and I've bought happily from them before (seems easier to tarnish a hard earned rep than build or re-build one)... but is this suspicious? And more importantly, what % bidding activity raises your radar.. 75%, 50%, 35%, 25%??? or is this even the key indicator?

Any advice greatly appreciated.