From the perspective of the buyer and the seller, if all goes well, there won’t be any difference. For example, when Mrs. Piper and I were in Paris over Christmas, it was my job to go out every morning to the local boulangerie to get the croissants and pain au chocolat. I went in, exchanged pleasantries with mademoiselle, placed my order, paid my euros, and went back to the appartement, where Mrs. Piper had made the coffee. (In case you can’t tell, I miss Paris… )
There’s no doubt a valid contract had been formed, but only a lawyer worries about such things in the abstract. As I said earlier, since the civil law and the common law both evolved in Europe, under an ever-increasing philosophy of freedom of contract and market economics, that’s not a surprise. Laws evolve to match social expectations.
It’s only if something goes wrong in the performance of a contract that issues might arise about the legal status of a contract. It’s also not likely to arise over a sale of a few croissants, because the stakes are so low. Issues about the validity of a contract are more likely to arise in a large commercial transaction, for example, if the baker ordered a month’s supply of flour, and the supplier didn’t provide it on time. If the baker has had to re-order the flour on short notice from another supplier, at higher cost, he might argue that he doesn’t have to accept the flour from the first supplier. The first supplier might counter that there was a reason for his failure to deliver on time, such as he thought the baker wanted the flour on a different date or something. And then, if they can’t resolve it, they may both seek legal advice. And it’s at that point that the differences in methodology between the two systems comes into play, as the lawyers start to work on their legal opinions.
In most civil law jurisdictions, the primary source of law governing the issue will likely be a civil or commercial code, supplemented by the authorities of learned writers. Court decisions may be consulted, but those decisions are not themselves considered to be statements of the law, simply the application of the law to the facts of a particular case. Depending on the practice in the courts of a civil law jurisdiction, the decision may be quite short and sparse, simply reciting the facts, the relevant sections of the Code, and a summary of the court’s ruling. Even in appellate cases, in some civil law jurisdictions there are no dissenting reasons by the minority judges.
If the same issue arose in a common law jurisdiction, there may be a statute governing the issue (e.g. - a state statute based on the Uniform Commercial Code in the U.S., or a provincial Sale of Goods Act in Canada), but it’s quite possible that there is no statute. In that case, the relevant law is found in the decisions of the courts, setting out the legal requirements for a valid contract to be formed, reasons for repudiation, and so on. Even if the jurisdiction has a statute governing the issue, the judicial interpretation of that statute is very important. The cases will go into the facts and the law in great detail, and the judicial commentary on the statute will be treated as essentially part of the law itself. Depending on the degree of detail in the statute, the court may find that the statute is not meant to displace the common law of contracts, but simply to supplement it, or change it some particular way. If so, court cases dealing with the law of contracts in general will also be relevant. If the decision is from an appellate court, there may be a dissent that needs to be studied, to see if there is likely to be a change in the law.
However, all that is in the lawyer’s office. The net product will be a legal opinion that the lawyer provides to the client, summarising the lawyer’s assessment of the client’s rights and obligations, and likely outcome if the matter goes to court. As I said with my Ford-Honda metaphor, the main differences between the two systems are technical and under the hood, where the mechanic (or lawyer) does the work in case of malfunction.