Are you just using the bog standard template? If so then set up your lisings using the Advanced Selling Form, as eBay don't tend to interfere with listings created using the Advanced Selling Form.
If you do try to do that then if eBay still continue to butt in and change your listings without your permission then there is another workaround opton that may well prevent the problem. Decide on how much you want for the item, then add onto that how much you're going to have to pay out for eBay and PayPal's cut of the selling price, then add on the postage and packing price.
Once you've done that set up the Best Offer option and activate both the "Automatically Accept..." and "Automatically Reject..." functions. When you're setting the "Automatically Accept..." feature up add the actual price that you would otherwise have listed as the Buy It Now price so that it is set up as the minimum amount you'd be willing to accept as a Best Offer. When you've done that go to the "Automatically Reject..." feature and add a price that's 1p below the amount that you added to the "Automatically Accept..." feature. Make sure that the Buy It Now price is set quite a bit higher than the amount than you actually want for the item - that way, if somebody commits to purchasing the item using the Buy It Now function then you could stand to make quite a lot more from the sale of the item than you otherwise may have done had you not used this tactic. If, however, somebody makes you a best offer then although your item won't sell for its displayed Buy It Now price then so long as somebody makes a best offer that's equivalent to, or higher than, the amount that you entered in the "Automatically Accept..." function then you should still receive an amount that you'd be happy with.
I know it might seem like a lot of hassle to have to set up another listing from scratch again in order to get around the problem, but sometimes you just have to use eBay's features to make it work against itself so that the end result works in your favour, and not in eBay's.
