B&W Nautilus 804s and clipping

Hello there - this is my first post and I'd be grateful for any help you folks can offer me.

I'm building my first home stereo setup right now after years of waiting. The first component will be a used pair of B&W Nautilus 804s which I've found for a pretty good price.

My question is this: how can I tell whether the speakers have suffered somehow due to clipping? The reason I'm worried is that the guy I'm buying from has been running them off a Harmon Kardon AVR-3000 receiver (with 50W output in stereo mode). Isn't this likely to have caused some damage if he's been working the amp too hard? If so, will the tweeter etc. sound noticeably different from normal or will they just completely fail to produce sound?

I was only able to audition them using his amp, not having yet bought my own. Is it necessary to hear these with, for example, a power amp to know whether they are in good condition sonically?

Sorry to labour the point(s). Hope some of you can help!
Everyone has their trick - firstly you need to be intimately familiar with the sound of a particular recording - I like well recorded piano and percussion as the best indicator of tweeter quality (as most tweeters compress all too easily and this is usually the problem). Dave Grusin's Hommage to Duke C-Jam Blues has some hard hitting piano notes. If they sound harsh or grainy or don't sound totally effortless at very loud levels then there might be a problem.

If it is any consolation tweeters are usually the cheapest driver to replace anyway. Replacement part availability should always be one of your considerations in a second hand purchase. Boys will often break their toys.
B&W's do not have a reputation of frying tweeters.
Tweeters either are burned out or ok. (usually/mostly)
B&W tweets are NOT cheap!
I would say if the tweets seemed to work they are gonna' be ok.
Occasional clipping is not going to damage the drivers. And when the drivers are damaged you'll notice right away. It'll either sound right or wrong. There is no middle state. B&W Nautilus tweeters are around $100 each.
Elizabeth...that's not true. The B&W's do have a reputation for tweeter troubles...and they are easy to repair. I had a 802 and went through 3 tweeter...they just delaminated. The tweeters were given to me no charge by B&W, but they would have charged me labor. I did it myself..a couple of screws, and done. No soldering required. When my tweeters went bad, they simply stopped working. Put your ear to the individual speakers and make sure there is sound coming out of all of them.
Thanks for your help, everyone. I feel a bit more confident about buying these now since various familiar CDs sounded fine right across the spectrum.
How much are you paying?
When testing the tweeter be sure to feed the speaker a signal that will truly test the tweeter. B&W sets there crossover for the tweeter rather high for the 800 series floorstanders. All vocals and 95 percent of the fundamental frequencies from classical music are actually handled by the midrange. B&W does a pretty good job of integrating the midrange with the tweeter but if you divert your ear from the midrange (i.e. hold a piece of foam or some other absorbing material at 90 degrees to the cabinet just below the tweeter and listen directly (close up) to the tweeter, you can find the source material that will be a good test disc. You may be surprised. Rock music with high end guitar riffs is the easiest source to test the tweeter,or a test disc with a range of tones. Of course once you find the proper source material then increase the volume and move back. If the tweeter is damaged and still 'works' you will hear it at high volumes -likely as a very noticible intermittent 'rasp' it will be obvious and will not require any guesswork. Just be sure to listen to your source material on a known good system beforehand. Much more common for the top mounted tweeter is damage that can be observed by careful visual inspection, tykes and inquisitive adults have a habit of 'pushing the button' - jamming their finger into the tweeter.
Thanks again for all the help. I'm now running these with a Musical Fidelity A300 and they are sounding great. There are no problems at all with the tweeters but, yes, I have noticed that they are not given much work to do compared to the other drivers.

Currently deciding on the best-sounding speaker cables and planning to buy a Rega Apollo pretty soon...