The doorway on Zaragoza Street was set back from the sidewalk. A small sign said simply. "Crafts - Ring bell." There were no display windows or other indications that commerce was practiced within. We had only the guide's assurances of "good shopping."

This could hardly be regarded as coming on strong with salesmanship, and accusation made against many Mexicans who deal with bargain-hungry American tourists. On the other hand, we weren't used to being led unerringly by a guide to a single store when shopping.

But Prof. Adolfo Becerril was no ordinary guide .

We had seen the worst kind of guides - the type found in any major tourist center - in Acapulco and Mexico City,and we ignored them. But when our party of four, traveling by automobile from the Mexican capital to Guadalajara, arrived here - the half-way point-our resistance apparently was low.

Morelia is a city of immense charm. It is colonial Mexican, nearly three centuries old, and many of the buildings remain as they were-but with some modern accoutrements. Our hotel-De La Soleda, $17 for a double room - was immaculate and its facilities were 1977 in every way, but without destroying the early 18th-century atmosphere and history (it had been a monastery).

So after driving through the city and reveling in the unique architecture and setting, and then finding our hotel thoroughly satisfying, we were mellowed for Becerril.

We set out to walk around the town and immediately came to the great twin-towered cathedral. No sooner had we entered than we became the property of the professor.

"You want to see this fine cathedral and all the treasures in it?" he asked. "I will tell you all the important things. Yes? Come with me. Of course it is beautiful. Now listen to meand you will learn," He assured us.

So we listened and learned for some considerable time and became the willing followers of the professor, who, it turned out, was a licensed guide and adopted the title of "professor" because he "helped teach some history courses at the university."

He spoke excellent English because he had lived in New York for some years, working in "Macy's and Gimbels and all those places."

When we finished the cathedral, the professor said, "Now you will want to go shopping. I will show you the way to the place you must go. Come."

Hesitating only the briefest of moments for an indication of assent, he turned and marched off. We followed, of course.

And thus we came to the doorstep of the Cerda sisters on Zaragoza Street. Maria Cerda answered the proffessor's ring and invited us in. We passed through a courtyard and entered a large room crammed with colorful and beautifully made handicrafts ranging from clothing to carvings.

The Cerdas are a large family of craftspeople who offer their creations in several areas of Mexico, including Guadalajara, Maria Cerda explained. In Morelia, the three sisters "and several cousins, etc.," as she put it, specialize in lacquerware and hand-stitched clothing.

Suffice it to say that we went slightly mad in the Cerda shop. The merchandise was beautiful and priced very reasonably. We made no effort to bargain and the Cerdas obviously did not expect to bargain. They expected to be paid a fair price for their creativity, but were not trying to gouge their customers.

We also found Cerdas in Guadalajara, specializing in fancily embroidered shirts, dresses and other clothing. They were plenty expensive, but the product was worth the price. Also in Guadalajara is perhaps the most reasonably priced, all-around shopping area with high quality goods in all of Mexico. It is Tiaquepaque, in the old section of the city, with block after block of excellent small shops offering a wide variety of merchandise.

Experience in shopping in Acapulco, Taxco (the silver center), Mexico City, Morelia and Guadalajara convinces me that the following guide is reasonbly accurate.

At the top of the scale are shops in or near the luxury hotels for tourists. The quality of the merchandise is excellent but the prices are exorbitant. Anyone who buys anything in those shops is foolish, extravagantly wealthy - or both. There is no bargaining. Clerks have no authority.

Next are the established shopping areas much like those in American cities, whether city blocks or shopping centers. Prices still are comparatively high, but not ridiculous. There is no real bargaining, but some places may allow a "discount." Depending on location, these may cater to tourists, or may simply be regular shopping areas for the Mexicans themselves. In the latter case, prices are less.

The market areas for the home folks are next. It takes much wandering around and examining of products, but good bargains may be found. You do have to be alert for the wise stall operator who may jack up prices a little when tourist is spotted, but these people are prepared to bargain and some seem to enjoy a spirited exchange.

On a previous trip to Mexico, I engaged in a bargaining bout with a woman in the Oaxaca market and ended up with four serapes at a cost nearly half of her original asking price.

As I handed over the money, the womaN beamed broadly, struck out her hand and said,"You okay,big fella!"

Then there are the street salesmen. Normally, nothing is wrong with the quality of the goods they hawk, but they insist they are giving you a bargain while they ask three or four times what the item can be purchased for nearly anywhere else. If Americans buy from these amiable but larcenous characters, they should offer about one-fifth the initial asking price and soon will find the bottom line (somewhere in-between) that gives the seller a fair profit.

Our best shopping experience was with the sisters Cerda, where we found utter honesty as well as high quality goods. They wrapped out many purchases so we wouldn't have to unpack them before we got home.

That evening, as we were dining in the striking medieval-style restaurant at the hotel, the waiter escorted someone to our table. It was Maria Cerda. She held out a small package. When straightening the shop, she had found that one of our purchases had been pushed aside during the wrapping.

She smiled at us and said she hoped we were enjoying ourselves. We were.