Hi,
I decided to make a new thread, to spare Leo any more semi off topic posts.
In Europe mark up is simply the difference between cost price (including taxes) and selling price (including taxes). It may be expressed in monetary terms or percentage terms with equal validity. If in percentage terms, it is calculated as a percentage of the cost price of course. Only discounts are calculated against selling prices.
A wine costing for example (tax, delivery etc paid) €3 may be sold in the restaurant at (say) €9.60. Mark up would therefore be €6.60. it could either be expressed as that (in monetary terms, therefore) or as a percentage of the original. (6.60/3.0)*100 = 220%. And as it happens, this is the minimum figure which the tax inspectors in France expect hoteliers to use (if they declare a lower wine profit than that, they have to prove it).
To coime to Leo's original question, I know a restaurant (admirable) which works on a fixed mark up (in monetary terms). They add €8 to the total cost price (including taxes) to them of any wine they sell. So a wine which costs them €3 they sell at €11, (a significant markup in percentage terms) but a wine which costs them €30, gets sold at €38 - a VERY good deal and an excellent way of encouraging people to drink better wines.
I also know of another restaurant which about 5 years ago sold a wine I bought retail at FF20 (call it €3) at the ludicrous price of FF140 (call it €21). As I don't know what price THEY bought it for (certainly way less than the €3 I paid retail in a wine shop) I can't say what the mark up would have been.
Finally, as to what is acceptable. Impossible to make any kind of intelligent answer. A restaurant employing a highly trained expert sommelier must charge a higher mark-up than one selling simple local wines. A restaurant paying taxes on stock, and which keeps wine for 10-20 years until ready to drink will inevitably have to charge a higher mark up to pay the taxes and for tying up capital than one which carries almost no stock and sells what they order within the year.