I can't help much with the differences between one Alpine or the other as I am a die-hard Kenwood e
Xcelon fan.
The
eBay I might be able to give a bit of insight into, though...
eBay's bidding system is called a
proxy bidding system meaning that you can bid any amount you want/need to but
eBay's automated system will only use as much of that bid as is necessary to get a step ahead of the highest underbidder. (ergo ~ you may place a bid of $300 on an item but if the highest bidder before you only bid $90 then
eBay will only use $91 of your $300 to get ahead of the other guy)
Some people will place a bid ten upon further consideration of said bid decide that it wasn't high enough and they will go back in and rebid (sometimes several times before they quit) to raise the maximum amount of their proxy. If a single individual is the highest bidder and goes back in and rebids, rebids, and rebids again all they have done is tell
eBay's proxy system to change the maximum amount that it is allowed to bid for them. It will
not change the actual high bid as you cannot outbid yourself within the
eBay format (I wouldn't suggest trying this in a live, "Going, Going, Gone!' type of setup, however....)
If two or more people have gotten into a bidding war (never a good idea as your emotional reactions to such a thing can easily overload your finances before you know what has happened) then you might see the high bid raise substantially in a very short period of time. I snipe bid myself, which is a somewhat controversial practice of waiting until the final 10 seconds of a listing before placing a bid thus eliminating the possibility of someone making a reactionary bid just to get back ahead of me.
Bid shilling, or placing a false bid on a listing to artificially raise the bids to a preferred level, does happen. If you do your research more often than not it's fairly easy to catch. Generally you'll see it on big-ticket items and the shill bidders will be the same usernames bidding on a certain seller's items continually but somehow managing to never win an item. Heaps of bids from brand-new usernames is a tipoff as well.
eBay can be a crapshoot if you do not do your reasearch first. I am very, very picky about with who and how I conduct business on
eBay and that pickiness has served me well thus far as I have *knock on wood*
never been scammed once to this point.